中文：

DDX指标是一种基于大单净差成交量的指标，它反映了主力资金的买卖行为。该指标通过计算大单净买入量与成交量的比值来反映主力资金的意图，当DDX指标为正值时，表示主力资金在买入，而当DDX指标为负值时，表示主力资金在卖出。

DDX指标的应用范围较广，可以用于股票、期货等交易品种的分析。通过观察DDX指标的变化，投资者可以了解主力资金的动向和买卖行为，从而更好地把握市场趋势和买卖时机。

然而，DDX指标并非绝对可靠的技术分析工具，它只能作为一种辅助分析工具使用。在实际操作中，投资者还需要结合其他技术指标、基本面分析等多种方法来综合判断市场的走势和买卖时机。

英文：

DDX is an index based on the volume of large net buying orders, which reflects the buying and selling behavior of main funds. By calculating the ratio of large net buying orders to the volume of transactions, the index reflects the intention of main funds. When DDX is positive, it means that main funds are buying, while when DDX is negative, it means that main funds are selling.

The application scope of DDX index is wide, which can be used for analysis of stocks, futures and other trading varieties. By observing the changes of DDX index, investors can understand the direction and behavior of main funds, so as to better grasp market trends and trading opportunities.

However, DDX index is not an absolutely reliable technical analysis tool, it can only be used as an auxiliary analysis tool. In practical operation, investors also need to combine other technical indicators, fundamental analysis and other methods to comprehensively judge the market trend and trading opportunities.