Objective To establish an ultrasonic viscoelastic detection system to measure the viscoelasticity of in vitro tissues. Methods Based on the method of shear wave dispersion ultrasound vibration (SDUV), this system applied acoustic radiation force to excite harmonic vibration in soft tissues. The propagation of shear waves induced by the vibration was detected and the tissue viscoelasticity properties were calculated. The standard phantom and rat liver experiment were conducted using this system, and preliminary assessment of the system was completed. Results The measured result of standard phantom was close to the calibration value. The viscous and elastic coefficient of rat liver were (1.12±0.41) Pa?s and (0.81±0.40) kPa, respectively. Conclusions The results about the standard phantom and rat liver experiment approved feasibility of the system for viscoelasticity measurement on in vitro animal experiment, which is a preliminary exploration for the realization of liver fibrosis detection of human body.