Shear yield stress is one of the main parameters reflecting the rheological characteristics of the magnetorheological fluid. The stable and controllable magnetic field directly affects the measurement accuracy of magnetorheologicalfluid shear yield stress. Therefore, the reasonability of magnetic field design has an important impacton the rheological performance testof magnetorheological fluid. In this article, a concave magnetic circuit is designed to change the magnetic field structure by adjusting the position of the coil. The magnetic field lines pass perpendicular through the flow direction of the magnetorheological fluid, and the detachable combined magnetic circuit design realizes the continuous measurement of magnetorheologicalfluid under the premise of ensuring the magnetic field strength. In addition, the distribution of magnetic field strength under differentcurrents is analyzed, and mechanical properties such as shear yield stress of magnetorheological fluid are tested based on the optimized magnetic circuit. Compared with the mainstream standard test instruments,the average relative deviation value of shear yield stress measured by the magnetorheological fluid test system with concave magnetic circuit structure is about 10%,and the repeat error is within 6.34%. Results indicate that the magnetic circuit structure is a feasible method for the design of magnetic field devices in magnetorheological test.