Aiming at the tracking question that one target changes to multi-targets,such as the separating of airplane and rocket,the separating of airplane and missile and the separating of classes,a complex target- identify arithmetic is put forward.It is based on target′s area,length,width,length and width ratio,compat degree,moment of inertia and flight path.This arithmetic can identify the target exactly.Among the arithmetic,a new primary and secondary objects switch technique are applied.The arithmetic heightens the multi-targets track reliability.The results show that the arithmetic is provided with high targets identify precision,good targets switch stability and high extend apply value.