Waterfall Line (PBX) is a main method of analyzing the trend of stock prices in the financial field, which was widely used in Europe and America in the early 1990s. Therefore, it is named as a waterfall when it converges and diverges downward. It belongs to the traditional trend line of general trend price. Its real name is the non-linear weighted moving average. It is composed of six non-linear weighted moving average lines. Each average line represents the cost of stock price in different time periods, which is convenient for comparative analysis.