After the occurrence of an earthquake, different surface features at different seismic intensity areas are exposed to individual degrees of damage. The quick obtainment of accurate seismic intensities and their spatial distribution is an important basis and parameter for the post-earthquake emergency rescue. To construct seismic intensity rapid reporting system as a cloud service applying cloud computing technology and provide scalable, configurable, transparent seismic influence field analysis application service, will be a new technology and trend for the development of seismic intensity rapid reporting systems. Based on a geographical knowledge cloud service system, namely GeoKSCloud, which is developed innovatively and independently by our research team, this paper carried out the design and implementation of a cloud service system for seismic influence field analysis. By taking Fujian Province as the study area, seismic intensity attenuation relationship and peak ground motion acceleration site correction method suitable for Fujian area are firstly analyzed, and then the working mechanism and workflow-based service composition of their cloud service are proposed. To implement the cloud service, related atomic services are realized, service-oriented packaged and published on GeoKSCloud system (such as seismic intensity attenuation calculation service, PGA site correction service, seismic site property obtaining service for grid points, service for coordinate transformation along the seismic attenuation axis direction for grid points, et al.), data services for supporting spatial datasets are published as well, and also a Web GIS based cloud service portal are developed and integrated with GeoKSCloud. Finally, an analysis case of seismic influence field analysis is carried out on the constructed cloud portal, with the offshore 7.5 earthquake occurred in Quanzhou area in 1604 as the real case. The peak motion accelerations (including bedrock PGA and ground PGA) for all equally spaced grid points within Fujian Province are calculated via the cloud service proposed. Based on the PGA values of the grid points, the spatial distribution of PGA values covered Fujian Province was also interpolated and further comparative analyzed with the actual survey data. The results show that, the seismic influence field analysis cloud service presented in this paper, which has taken account of the site-specific amplification effecting, can provide more precise seismic influence spatial distribution than the traditional method which consider only the seismic intensity attenuation relationship. The cloud service system with distinct advantage features of cloud service, such as scalable, configurable and transparent, would provide a common technology and a support service platform for intensity rapid reporting system research and application, and also give an innovative operation pattern for public service of seismic intensity rapid reporting.