The preceding-evaluation plays a crucial role in guiding construction. Preceding-evaluation system of rural drinking water safety project includes four main contents: opportunity evaluation, necessity evaluation, feasibility evaluation and decision evaluation. Using multi-turns specialist consultation method, the paper mainly studies the decision evaluation. Modular system structure is designed according to system function analysis and target analysis. Based on system database as the basic information support, preceding-evaluation system is developed by object-oriented method. The syetem includes the functions of project information storage, project estimation, economic analysis and decision evaluation, it can provide reference for planning, design and construction management of rural drinking water safety project.