Allocation standard and decision method of ancillary service under the power spot market situation are the key factors to the coordination of economy and reliability of system operation. This paper analyzes the present application of power ancillary service at home and abroad and the mechanism theory of Guangdong ancillary market. Based on the facts of spot market construction in southern region of China (starting from Guangdong), the development path by stages of ancillary service market is proposed. Starting from the present management condition of ancillary service and on the premise of the system reliability, market mechanism is gradually utilized to enhance the rationality and economy of ancillary service decision, which meets the demand of coordinated operation of electricity market and ancillary market. In consideration of market allocation mechanism and compensation standard, ancillary service market construction schemes in each spot market development stages are also designed, which provides reference for ancillary service market mode and its mechanism design in southern region of China.