Multi-tenant is the core of cloud computing, it solves the problem of sharing system resources and applications among multiple users, and improves the utilization of software and hardware of a system. How to improve server utilization without degrading the quality of tenant service is a challenging problem. This study suggests a rural drinking water survey database system based on Eucalyptus platform and multi-tenant technology. Data storage uses the sharing mode of shared database, and this paper discusses a Multi-tenant Improved Genetic Placement Algorithm (MIGPA) which places tenant in a proper location in a virtual environment with minimum consumption of hardware resources and guaranteed service quality. Experiment results show that the algorithm is feasible and effective.