In order to research the rheological property of MRF at high shear rate, a magnetorheological fluid (MRF) rheological property testing device based on valve mode is developed. The accurate analytical expressions of MRF rheological parameters in terms of structural dimensions of testing device and pressure gradient in the damping channel are derived, and the flow State of MRF is considered, which provides the theoretical foundation for testing the rheological property of MRF at high shear rate. The relationship between magnetic indication in the annular channel and excitation electrical current is experimentally obtained. Some elements influencing testing are analyzed and eliminated. The device is used to test the rheological parameters of MRF, and the results show that the yield stress of MRF falls off significantly as the piston velocity continues to increase. The shear rates in designed device may exceed 2.5×105/s, which meets the special demands in MRF testing.