A new method based on the measurement of velocity of laser-generated ultrasound is proposed to determinate the second order elastic (SOE) constants and density of isotropic materials. A serial of ultrasonic pulses can be detected by self-made PZT transducer fixed in the detection point when scanning the line source focused from NdYAG laser with electronic control translation stage. Then the velocity of Rayleigh waves is computed by waveform cross-correlation technique; the velocities of longitudinal wave and shear wave reflected by the bottom surface of the sample are obtained by different traveling time with their propagation distance. At the end, the SOE constants and density of isotropic material are determinated according to the Christoffel theory of elasticity. Results show that the values of SOE constants and density which signed with C11, C44 and ρ agree well with the corresponding parameters reported in the existing papers. What′s more, the relative accuracy of the determinated parameters indicated from error analysis demonstrates the feasibility and reliability of this method.