In order to quantitatively analyze and evaluate the longdistance guidance effectiveness of the Early Warning Aircraft steering the fighter, the longdistance guidance successful probability is taken as an index for describing the guidance effectiveness, and a mathematic model is built up based on analyzing the course of the Early Warning Aircraft steering the fighter. And the course of longdistance guidance is divided into level guidance and vertical guidance, error analysis models of the level guidance and the vertical guidance are built up according to the parallel approach guidance rule, and the algorithms for longdistance guidance effectiveness are put forward by using probability analysis method, through the algorithm the relations are acquired between the longdistance guidance effectiveness and some factors such as guidance error, the fighter radar capability and target characteristic. Under the scene of the fighter lower speed than the target, an example of a fighter intercepting a target by the Early Warning Aircraft's longdistance guidance is given to analyze effect rules of primary parameters on longdistance guidance probability, including target enter angle, intercept distances, antenna scan area and target parameters precision. Through simulation the results efficiency approaches are presented for increasing the longdistance guidance effectiveness based on this scene