In view of the problem that the test cost is increased by a large number of test suites in regression testing, a test suite reduction method based on weak mutation criterion was proposed. Firstly, the relation matrix between test suites and mutation branches was obtained based on weak mutation criterion. Then, four invalid test requirements and subset test suites were reduced repeatedly. Finally, the current optimal test suite was selected by using artificial fish swarm algorithm, and the simplification and test suite selection operations were performed alternately until all the test requirements were covered. Compared with Greedy algorithm and HGS (Harrold-Gupta-Soff) algorithm on six classical programs, when using weak mutation criterion with no changing or slightly changing mutation score, the reduction rate was improved by 73.4% and 8.2% respectively, and the time consumption was decreased by 25.3% and 56.1% respectively. The experimental results show that the proposed method can effectively reduce the test suites and save the test cost in regression testing.