Active distribution network system has the characteristics of complex structure，high DGpermeability，large load fluctuation，strict control requirements. The data information of operation has thecharacteristics of high volume，high speed，diversity and value. For active distribution network data processing，according to the theory of cloud calculation，using the data mining technology and distributed parallel computingmethod，establishing an active distribution network security monitoring system model based on PDMiner large datamining platform. The processing of historical data and real time fault data are studied respectively. Research resultsshow that the system by processing of historical data for risk zoning，development planning，operation stateevaluation，by processing of fault data for fault analysis and processing，providing the basis for the distributionnetwork security. The result of the system is verified by the simulation example.