MC/DC is a coverage criterion for the verification of avionics software of Level A, which can massively lower down the number of test cases. This paper focuses on the research of the logical expression with coupling conditions, and studies how to obtain the test case set as small as possible. It proposes two solutions which can be used respectively to solve the problems under the conditions of zero-coupling/weak-coupling and strong-coupling, and related examples are showed. The result shows that flexible usage of the two algorithms can solve the problems of rapid generation of MC/DC test case set for general logic expression.