The invention mainly relates to the technical field of machining, and discloses a surface treatment method for a motor case of a washing machine. The method comprises the steps: coarse grinding, fine grinding, washing, and coating. The method is simple, facilitates the operation, enables the roughness to be reduced to 0.13 microns, and enables the surface of the motor case to be smooth and repellent to water. The method enables a person to place the washing machine in a bathroom safely, enables the service life of the motor of the washing machine to be prolonged by 34%-36%, and improves the use performances of the washing machine. The coarse grinding of the motor cause, produced through casting, of the washing machine is carried out at first, so as to reduce the roughness of the motor case and to improve the work efficiency; and then the coarse grinding part is frozen for a long time and then the fine grinding of the coarse grinding part is carried out, so as to reduce the fine grinding difficulty and the heat generated by fine grinding, speed up the grinding speed, and maintaining the metallic luster of the motor case. The temperature of the motor case is quickly increased after fine grinding, and then the motor case is placed in hydrochloric acid solution, thereby achieving the quenching of the motor case, improving the strength and glossiness of the motor case, removing the dirt on the motor case, facilitating the subsequent processing, saving the operations, and improving the processing efficiency.