The invention provides a device and a method for testing the high-shear rate rheological behavior of a magnetorheological fluid. The device comprises a cylindrical housing, wherein the upper end and the lower end of the housing are respectively provided with an upper end cover and a lower end cover; the housing is internally provided with a piston, the housing is internally divided into an upper cavity and a lower cavity, the piston is inverted barrel-shaped, the bottom surface of the piston is opened, and the top surface of the piston is provided with a normal through hole; a piston rod is arranged in the piston in a penetrating manner, and the piston rod is arranged in the upper end cover in the penetrating manner to the outer part of the housing; a part of the position rod, arranged in the piston, is provided with a magnetic core in a winding way, the upper part of the magnetic core is provided with a coil in a winding way, and the coil is electrically connected with the outside through a conducting wire; the diameter of the lower cross section of the magnetic core is slightly less than the lower inner diameter of the piston to form a ring-shaped damp gap; the upper part of the upper cavity is provided with an upper oil pressure sensor, and the lower part of the lower cavity is provided with a lower oil pressure sensor; and the housing is internally provided with a temperature sensor. According to the device and the method, the influence of friction force on a test result can be removed, the influence of temperature factors can be sufficiently considered, and the device and the method have the advantages of being high in shear rate and exact in result.