Principle: Use the relative position of the current stock price in the recent stock price distribution to predict the possible trend reversal. It is a technical tool that mainly uses the real amplitude of price fluctuation to reflect the strength of price trend and the phenomenon of overbought and oversold, and sends out buying and selling signals before the price rises or falls. It was first used in the analysis of futures market, and then widely used in the short-term trend analysis of stock market. It is the most commonly used technical analysis tool in futures and stock markets. The colors of KDJ indicators in various softwares: K line is white, D line is yellow, and J line is purple.