In order to get better 3D photoacoustic tomography, focused ultrasound transducer is used to detect the photoacoustic signal of ring source excitation, then the filtered back projection algorithm, finally the 3D photoacoustic tomography of simulated blood vessel and carbon was formed by Volview software. The simulation and experimental results show that the image comes in true with high resolution and good contrast using the method, and the reconstructed images are in good agreement with the real objects in the 3D image. The YAG laser source has a wavelength of 780 nm, repetition frequency of 10 Hz, pulse width of 16 ns, the PA signal detector is a cylindrical focused ultrasonic transducer, with a receiving diameter of 3 cm.