To improve the anti-interference and stealth capability of surface-to-air missile system, a synergistic operating mode, i.e., the passive radar tracking system with assistance of active radar, was proposed based on the advantages of both the active and passive radars.A new cooperated detecting and tracking algorithm was designed based on the mode.The operation of the active radar was controlled in real time by introducing the fuzzy reasoning function and using the new practical variance and the change rate of measure error variance as input control variables.This method could not only control the active radar precisely and in real time, but also improve the system tracking precision.Monte Carlo simulation demonstrates the rationality of the synergistic operation model and the availability and correctness of the improved algorithm.