Abstract: The problem of test generation for sequential circuits belongs to the class of NP-complete problem. Due to its complexity test generation for sequential circuits always focuses on the single-clock circuits. However there are many non-synchronous circuits with multiple clocks or internal clock structures in the industrial applications, which could not be handled as the traditional synchronous circuits. In this paper, an orbicular model is presented which introduce the clock signal to the circuit model for test generation. Then a test generation flow for non-synchronous circuits is built up. By this approach, the non-synchronous circuits can be represented in synchronous models in order to utilize the synchronous sequential test generation directly.