I have recently been reviewing some classic technical indicators and found that many traders' understanding of the KDJ indicator still remains superficial. This tool, known as one of the "Three Treasures of Retail Investors," indeed has its unique power, but the key is to truly understand how to use it.

Let's first talk about the essence of the KDJ indicator. It is actually a stochastic indicator composed of three lines—K (fast line), D (slow line), and J (direction-sensitive line). Among them, the K and D lines are mainly used to judge overbought and oversold conditions, while the J line reflects the degree of deviation between the K and D lines. In theory, when the K line breaks above the D line, it indicates a possible upward trend; conversely, a downward crossing signals a decline.

I won't go into the detailed calculation here, as trading software usually handles that for us. The typical parameters are (9,3,3); higher values mean lower sensitivity to price fluctuations. In practical application, we usually draw two horizontal lines at 80 and 20 to determine overbought and oversold states.

What impressed me most was the market trend of the Hong Kong Hang Seng Index in 2016. In early February, the Hang Seng kept falling, and many were bearish, but traders who understood the KDJ indicator noticed a key phenomenon—that while the stock price made lower lows, the KDJ indicator was making higher lows, a classic bullish divergence pattern. As a result, on February 19, the Hang Seng Index shot up with a large bullish candle of 965 points, a 5.27% increase. Then, on the 20th, a low-level golden cross appeared below, which was another clear buy signal. On April 29, a death cross at a high level appeared, and smart investors took profits and exited. By the end of December, a double bottom pattern re-emerged, presenting another excellent entry opportunity. This case perfectly demonstrates the practical application value of the KDJ indicator.

There are several core trading signals. The golden cross refers to when the K and J lines simultaneously break above the D line, which is a buy signal. The death cross is the opposite—when K and J lines break below D, signaling a sell. Additionally, divergence patterns like top divergence and bottom divergence are also important—when the stock price hits a new high but the KDJ indicator declines, or the stock hits a new low but the indicator rises, it often indicates a trend reversal.

There are also some pattern signals worth noting. For example, when the index is below 50, the appearance of W bottoms or triple bottoms suggests a potential reversal upward; when above 80, M tops or triple tops indicate a possible decline. The more bottoms, the larger the rise; the more tops, the larger the fall—a simple rule.

However, I must honestly say that the KDJ indicator also has obvious shortcomings. First, it is prone to becoming dull, frequently giving false signals in extremely strong or weak markets. Second, it has a lagging nature because it is based on past price data; when the market changes rapidly, its response is not timely enough. Third, it can generate false signals, especially in sideways or choppy markets, where its performance becomes unstable.

Therefore, my advice is not to rely solely on the KDJ indicator for decision-making. The most reliable approach is to combine it with other technical indicators, such as candlestick charts, volume, and other information, to make a more comprehensive market judgment. In practice, fully utilizing the advantages of the KDJ indicator and using experience to compensate for its shortcomings is the most important thing in trading.