The [011] polarized PIN-PMN-PT crystal cut in the zxt±45° direction has wide applications prospects in the field of underwater acoustic transducers due to high piezoelectric coefficient, high compliance coefficient and electromechanical efficiency. Compared to the traditional Tonpilz transducers, in this paper the relaxation ferroelectric single crystals with free face shear mode are located between the radiation head and the tail mass. The influences of geometry parameters on resonance frequency and emission voltage response were investigated. The simulation results show that the working frequency bandwidth of the transducer is from 9 kHz to 62 kHz, and the maximum emission voltage response is 137.5 dB with a fluctuation of about 4 dB. Thus, the free face shear mode is beneficial to achieve the small size, high power and broadband transmission of the underwater acoustic transducer.