A novel structure for piezo resistive ultrasonic transducer is introduced, which consists of main vibrate cantilever and mini sensing cantilever. The main cantilever vibrates under acoustic pressure and drives vibration of mini cantilever. Sensitivity has been analysis by Ansys. Result shows that the sensitivity of mini cantilever has been improved compared with piezo resistance cantilever. To optimize the structure, relation between structure size and resonant frequency has been simulated. Static analysis on the mini cantilever with same resonant frequency has carried on. Sensitivities of different size mini cantilevers are calculated and compared to get the best sensitivity structure, and to accomplish optimization of the structure.