It is difficult and inefficient to detect curved surface thin plate parts when we adopt conventional ultrasonic testing method. Flexible comb transducer, which can excite certain mode guided wave, can be used for the problem to complete the curved surface micro crack detection rapidly. But because of multiple modes when guided waves propagate in thin plate structure, the propagation law is complex. Considering controlling the excitation guided wave mode in such parts, we can obtain good detection effects. This paper carries out the guided wave mode control research in the process of excitation. We summarize the method to control the guided wave mode, and design the verification experiment by using fixed finger spacing comb transducer to excite the certain mode guided wave in the given thickness aluminum plate.