The conformance testing of communication protocol is the process to evaluate whether the protocol implemented is identified with standard specification. By evaluating how generated test cases detect many faults, it can be used with standard estimating efficiency of conformance testing. The method that evaluates the capability of fault coverage for test cases, has been researched by mathematical analysis and simulation. In this paper, we pointed out the problem of existing method and proposed new evaluation model of fault covergage for test case which generated by foult model. Also, we analyzed the results comparing to the existing evaluation method and proved its validity.