The invention belongs to the technical field of power transmission line steel pipe pole cross-arm testing devices. A movable cross-arm mechanical property testing device comprises a testing platform, a fixed base, a pulley, a guide chain fixing member, a guide chain and a wire rope. The fixed base is arranged on the testing platform. The fixed base is connected with a tested cross-arm base flange through bolts. The pulley and the guide chain fixing member are arranged on the lower part of the testing platform. The testing platform is provided with a plurality of holes. One end of the wire rope penetrates through the hole to be connected with a tested cross-arm wire hanging point, and the other end is connected with the guide chain. The guide chain is connected with the guide chain fixing member. The movable cross-arm mechanical property testing device can carry out texting in a production workshop, workshop equipment is fully used for hoisting and the like, the testing difficulties are reduced, the testing schedule is accelerated, and no special testing field is needed. Compared with a conventional method, the working efficiency can be increased by more than 60% by using the method provided by the invention.