The invention discloses a water cooling structure for servo motor. The housing of the servo motor is provided with a plurality of water flowing channels arranged at intervals circumferentially in the direction of the parallel output shafts wherein two water flowing channels are connected with a first water inlet and a first water outlet respectively; the water flowing channel in connection with the first water inlet is in communication with an adjacent water flowing channel through an independent transition groove on the flange cover at the motor housing side and is in communication with the various water flowing channels sequentially through the independent transition grooves on the flange covers at the two ends of the motor housing alternatively until the various water flowing channels are connected with the water flowing channel. The independent transition grooves are groove bodies on the flange covers that only connect the end parts of two adjacent water flowing channels. The water cooling structure of the invention can meet the requirements for low vibration, low temperature rise and low noise of a large power motor and is also highly effective, energy conserving, environmentally friendly and can be conveniently manufactured.