Turning gear is a safety protection device for cracking gas compressor unit. During the single test of the steam turbine of a cracking gas compressor unit of an ethylene plant, the turning gear was operated normally. When the compressor unit was turned up after the combination of steam turbine and compressor through the coupling, the turning gear shook back and forth, and the compressor rotor could not rotate normally. The turning gear could not meet the turning requirements of the compressor unit. In this paper, the problems in the starting process of the turning gear of cracking gas compressor unit in ethylene plant are analyzed in depth, and a corresponding solution is put forward. By lowering the rotating speed and increasing the starting torque, the normal operation of the turning gear of compressor unit can be ensured.