A brake structure for a main shaft of a direct drive torque motor comprises a body, a direct drive torque motor, a main shaft and a brake assembly. The main shaft is provided for fixing the torque motor and the body, and the brake assembly is mounted between the body and the main shaft. An annular brake oil room of the brake assembly is positioned against the main shaft, and the brake seat subassembly has a thinner brake deformation wall formed between the annular brake oil room and the main shaft. The annular brake oil room utilizes its high pressure caused deformation to the brake deformation wall, thus achieving a braking effect by pressing the main shaft. Thereby, the present invention is easy to assemble, and not only can stop the main shaft quickly, but also has a greater locking force.