Abstract: To improve the test efficiency, a reduction method of test sets reduction based on set covering was presented. Redundancy reduction on the test set generated by Wp (part of W) method was carried out, which was a classical test generation algorithm in FSM (finite state machine) model. By analyzing the characteristics of Wp method, the regularity of the inclusion relations between test sequences was found, and then redundant test cases were deleted. Theoretical analysis and experimental results show that the method can effectively reduce the original test set and has the same error detection capabilities as the test set before.