The spatial grid data,with characteristics of the fast calculation and simple procession,are suitable for the pre-earthquake loss prediction or post-earthquake emergency loss assessment. As the earthquake loss assessment need a large amount of spatial grid(1km cell size)data set in nationwide such as seismic hazard,population,building area,and vulnerabilities of life and building hitted by earthquake. According to the principle of earthquake loss prediction,a solution is prepositively used to assess deterministically the losses of each grid cell with different intensity of seismic ground motion by optimized algorithm. Then a software system is designed and developed,supported with GIS functions,to realize the core functionalities including risk assessment related gridding data in 1km cell size. We therefore could get earthquake losses assessment and prompt post-earthquake losses assessment for response,etc. The earthquake loss of Chinese mainland from 2016 to 2025 is assessed in each 1km grid cell according to the system. The results show that the assessment efficiency is significantly improved. It provides us a practical tool for earthquake losses assessment and also shows better application to prompt assessment of loss after an earthquake.