The KDJ indicator is a commonly used technical analysis tool that helps traders identify market trends and optimal entry points through its three lines: K, D, and J. This article provides an in-depth analysis of the KDJ's operating logic, calculation methods, and practical application techniques, including overbought and oversold judgments, golden cross, and divergence patterns. It also points out its limitations and recommends combining it with other indicators to improve trading effectiveness. Mastering the skills to use the KDJ is the starting point for traders' success.