Abstract:A new formal method named path overlapped method is proposed for protocol conformance test generation based on UIO sequences. The main idea is to find a path without repeating transition in FSM as a POTS(path overlapped transition sequence), which is a sequence of distinct transitions such that if it is followed by a UIO sequence for the end state of the last transition in the sequence then all the transitions in the sequence are verified. According to the theoretical and experimental results, the test sequences generated by the path overlapped method are substantially shorter than those generated by other methods employing UIO sequences. Particularly, because of employing path overlapped transition sequence as a substitute for FOTS (fully overlapped transition sequence) in OUIO, generation time of overlapped sequence is greatly decreased.