In order to correctly assess the overall threat of enemy targets to the coast-sea joint air defense network, the index and its membership degree of threat assessment of incoming targets are constructed, and the subjective and objective combination weights of the index are given based on group AHP and improved entropy weight method. The threat degree of the target relative to the single defense platform and the whole defense network is given by the technique for order preference by similarity to ideal solution. The simulation results show that the threat assessment system is effective.