It is a feasible method to improve network security from user terminal s security.But when evaluating the user ter minal s behavior using trust degree, the judgment matrixes are usually acquired according to expert experience, and not much considera tion of environmental factors on the impact of the judgment matrixes.This paper presents an algorithm to solve the judgment matrixes compatible with the environment based on genetic algorithm,which can obtain a more accurate and scientific trust degree to assess the user terminal s behavior.Finally, experiments show that judgment matrixes gained by above-mentioned algorithm are compatible with the environment.