With the increased attention to the significant impact on the environment, consideration of the extent to which building impacts the environment is becoming a topical issue. In this paper, the emphasis was given to the development of a quantitative life-cycle environmental impact of building assessment system termed BEPAS (Building Environmental Performance Analysis System). BEPAS assesses quantitatively the environmental impact in the whole life cycle. BEPAS divides the model into three functions - facility operation, building material and site layout. By this system, two synthesis indices-pollution strength and economic pollution strength can be obtained, which can help the designers to optimize the design that strike a balance between environmental and economic performance This paper also presents a case to illustrate how BEPAS works.