The invention relates to a device used for testing magneto-rheological fluid shear yield stress. The testing device mainly comprises an adjustable uniform magnetic field generating device, a steel barrel, a rotary shaft, a seal ring cover plate, a support, a motor, a torque sensor, a Hall piece, a data demodulation single-chip microcomputer and a testing display instrument. The testing device has the advantages that the magnetic field generating device can generate a large adjustable uniform magnetic field; wall face sliding can be prevented from occurring to magneto-rheological fluid under the condition that the magnetic field exists; a testing and displaying device enables weak voltage difference signals to be output onto the testing display instrument accurately in real time through a torque sensor, the PWM theory, a signal amplifying circuit and A / D conversion; a low-reluctance closed loop is formed on the outer side of a close-wound coil through industrial pure iron, and a coil fixing frame on the inner side of the close-wound coil is made of nylon materials so that more magnetic lines can pass through the magneto-rheological fluid. The magneto-rheological fluid is arranged in the center of the magnetic field generating device, so that the magnetic induction strength generated by the detected magneto-rheological fluid is distributed evenly and perpendicularly.