Abstract: In view of the problem arising when the air—defense missiles and the artillery fight in coordination in the air defense operations，it analyzes the shooting pathway characteristics，velocity characteristics and the variation curve of the horizontal range of the air defense missiles and pellets．The research reaches the conclusion that if the air．defense missiles and the artillery are used to resist the same target，there will be pathway overlapping and the mutual disturbance of missiles and artillery ，thus affecting the air defense operation．To resolve this problem ，it advances the compatible conditions for avoiding firepower conflicts，and proposes the method of simulating and calculating the critical time when the two kinds of weapons are used together，which is of practical value to the study of the air defense operation．

Key words: fight in coordination；pathway；critical time