The landing gear buffer will absorb the energy caused by collision more than 80% when the Aircraft landing.In order to improve the performance of landing gear landing buffer, a kind of MR damper to replace the traditional hydraulic oil by using new type of intelligent materal of magnetorheological fluid was put forward. The influence of magnetic field on the design of MR damper was analyzed by using Ansys software.The results of theoretical and numerical calculation show that magnetic circuit structure design of MR damper is correct and effective.