The invention discloses an automatic demand response system and an automatic demand response method based on a cloud computing PaaS platform. According to the automatic demand response method, data needed by automatic demand response are processed, analyzed, dug and predicted by the cloud computing PaaS platform, and user power consumption information is rapidly computed by the aid of powerful data computing capability of cloud computing; the cloud computing PaaS platform provides an application program deployment environment, and power consumption data are computed by the cloud computing PaaS platform. The automatic demand response system comprises a user, a data collection system, a cloud computing resource pool, the cloud computing PaaS platform and an automatic response scheme module. The automatic demand response system and the automatic demand response method have the advantages that power consumption data computing capability is improved, automatic demand response speed is increased fully and real-time performance and accuracy of automatic demand response schemes are improved fully; cost is saved, and resource utilization rate is increased.