This thesis describes the key techniques of mode s ( selective ) , basic concept and its implementation . the respondent technology of mode s is based on the 24 bits address identifier of a plane , which could be used to detect the plane by the datalink , get the planes ’ property to identify , deal with the overlapping of several planes ’ replies 模式s的應答技術建立在對飛機的24位地址進行身份確認的基礎上,能用更好的鏈路預測來探測飛機,而且能同時得到有助識別飛機的屬性數據,能夠處理多架飛機應答數據交疊的情況。