The data processing capability of the SCADA master station directly affects the efficiency of system application in power system automation. The power system， especially the distribution grid， contains massive information. Aimed at the limits to the traditional SCADA system in the processing of massive information， an asynchronous invocated architecture for the SCADA service is proposed， with which the unprocessed data can be stored in the memory in a first in first out（FIFO） sequence for processing. This method ensures that no event will get lost when handling massive information. Based on the B/S structure and common information model（CIM）， the asynchronous SCADA system is implemented on the .Net platform. The avalanche test results of massive data processing and the field test operation are proof of its high performance and availability.