Abstract: In order to rebuild the pressure distribution from the schlieren image of focused ultrasound field directly, relationship was presented firstly between the spatial distribution of sound pressure and the intensity of schlieren image getting by Zernike phase contrast system based on the acousto-optic effect. Then the real-time sound image of focused ultrasound was obtained by the schlieren system. Due to the physical property of schlieren system, the spatial sound pressure distribution of a concave spherical shell focused ultrasonic transducer could be reconstructed by using a back-projection reconstruction algorithm lastly. According to analysis，when the electric power is 12 W, the horizontal size of reconstruction focal region is 0.25 mm closest to the theoretical 0.15 mm and when the electric power is 30 W, the acoustic axis size of reconstruction focal region is 1.35 mm closest to the theoretical 1.4 mm. Results compared with the theoretical sound pressure distribution of the spherical shell transducer show that this method has certain feasibility for ultrasonic transducer measurement.