For air-raid target the surface warship threat assessment is the basic foundation of firepower organization. To solve the shortcomings of traditional approximation method, Technique for Order Preference by Similarity to Ideal Solution (TOPSIS), for order preference by similarity to solution in calculating the weights, an improved TOPSIS based on entropy was applied to the multi-target threat problems with weights unknown. This algorithm used entropy theory to process air-raid target objective information, determined each attribute weights of the goal. Then, the weights were applied to the TOPSIS model, and the evaluating model and algorithm of multi-target threat which based on modified TOPSIS model were given. The method is proven to the reasonable and valid by the practical example.