止损单是交易者设置的自动下单或平仓的指令——当价格位于特定的价位，买或卖的指令即被下达。交易者所遵循的首要交易纪律是：限制损失。止损单就是为了方便交易者限制潜在的损失，设置在多单的下部和空单的上部。
例：如果你在$90.00买入1，000股IBM股票，你可以在以下位置设置止损：
当IBM股价低于或等于$87.00时，将手中的1，000股平仓。
如果价格达到 $87.00，那么你的止损指令将会被触发。
加上佣金，你每股的损失被限定在$3.00。
通常，市场缺乏流通量时会导致极端的价格波动，应该避免在这种情况下交易。
止损单的种类
• 市价止损单（Market Stop Orders）
是一种常见的止损指令，指的是一种当市场价格达到某一特定水平时买进或卖出的指令来减少自己的亏损。
• 限价止损单（Limit Stop Orders）
止损限价单指令系统在用户指定的止损触发价格被触碰或超越时提交一份买或卖限价单。
• 固定价止损单（Fixed Price Stop Orders）
定价止损是当价格达到某一水平时触发止损。一些交易所称它为限价止损，因此在交易前要确认所采取的止损种类。
在入场之前，推荐使用限价止损单：与定价止损单相比，限价止损单被执行的可能性更大。并且限价止损单没有市价止损单的开放性（不论市价是多少，你的单子都将被执行）。
平仓时建立采用市价止损单：保证你的单子尽可能地以最优价位执行。如果价位迅速下跌，不要抱着价格将会反转的希望，而是应该需立即平仓。埃德温•勒菲弗在股票作手回忆录中总结了一个困境：“他们开始时不愿意承担一个小小的损失，而是继续持仓，并希望在收支相抵时出场。然而，价格却在接连不断的下跌，损失也越来越大。似乎唯有继续持仓才是正确的选择，因为价格在一年左右肯定会回到该价位。随着价格持续走低，越来越多的人抛售，最终，不管他们愿意与否，都会被市场强制出局”。
止损指令的评价
止损指令并不总是完美执行。如果一个主要的支撑位被打破，大量的止损单会在同一时间被触发。卖方远比买方多，导致价格猛跌，导致卖出指令不能被执行。极端情况下，甚至会没有买方的出现。
尽管止损指令不完美，但确能有效的将损失限定在一定范围内，并保护资产的流失。如果所交易的市场中没有止损，那么设置自己限价单并从经纪商订制短信提醒服务。另外，止损需要毫不犹豫的自律性。
所需的步骤
1.首先，确定你可接受的最大损失;
2.基于良好的技术水平设置止损水平;
3.不断的调整你的止损水平，锁定利润;
4.使用跟踪止损来确定进出市场的时间。
Stop Loss Orders
Stop loss orders ("stops") are limits set by traders at which they will automatically enter or exit trades - an order to buy or sell is placed in the market if price reaches a specified limit.
The first discipline that any trader should master is to always limit your losses.
A stop loss order is set to limit a trader's potential loss. The stop loss is placed below the current price (to protect a long position) or above the current price (to protect a short position).
Example: If you purchase 1,000 IBM at $90.00 you may decide to place a stop loss as follows:
SELL 1,000 IBM IF price is less than or equal to $87.00
If price falls to $87.00 your order will be activated.
Your loss is limited to $3.00 per share (plus brokerage).
As a rule: avoid markets with low liquidity where extreme price fluctuations are possible.
Stop Loss Order Types
• Market Stop Orders
This is a conventional stop loss order - the stop activates a market order to sell (or buy) at the prevailing market price.
• Limit Stop Orders
The limit stop activates an order to sell at the prevailing market price but not below a specified limit (or buy at the prevailing price up to a specified limit).
• Fixed Price Stop Orders
The stop loss activates an order at a fixed price. Some exchanges refer to these as limit stop orders so check that you are using the correct stop loss order.
Limit stop orders are recommended for entering a trade: they have a greater chance of success than fixed price orders but are not as open-ended as market orders (where your order will be executed no matter what the market price is).
Market stop orders should be used to exit trades: to ensure that the order has the best possible chance of execution. Never hold on to securities if price falls sharply - in the hope that they will recover. Edwin Lefevre sums up the predicament in Reminiscences of a Stock Operator :
It was the same with all. They would not take a small loss at first but had held on, in the hope of a recovery that would "let them out even." And prices had sunk and sunk until the loss was so great it seemed only proper to hold on, if need be a year, for sooner or later prices must come back. But the break "shook them out," and prices just went so much lower because so many people had to sell, whether they would or not.
Evaluation of Stop Losses
Stop loss orders do not always work perfectly. If a major support level is breached, a large number of stops may be activated at the same time. Sellers will far exceed buyers, causing price to fall sharply and leaving sell orders unfilled. In extreme cases there may be no buyers at all for a security -- not at any price.
Imperfect as they are, stops are still an effective mechanism for limiting risk and protecting capital.
If stops are not accepted in a market, set your own limits and place buy or sell orders when the price is reached. Use SMS alerts if they are available from an online broker. Self-discipline is required to execute stops without hesitation.
Steps Required
1. First, determine your maximum acceptable loss;
2. Set stop loss order levels based on sound technical levels;
3. Adjust your stop loss levels over time to lock in profits;
4. Use trailing stops to time your entry and exit from the market.
本文翻译由兄弟财经提供
文章来源：http://www.incrediblecharts.com/trading/stop_loss_orders.php