Abstract: Environmental impact factors of green construction are identified in different construction stages by using the method of process analysis，and the evaluation system of green construction environmental factors is established． The weight sequence is calculated by using the improved analytic hierarchy process ( IAHP ) and the influence degree model of important environmental factors is set up，then the environmental impact factors in different construction stages are evaluated． Based on the theories and methods mentioned in the paper，a project of green construction in Nanjing is given as a calculation example． Result shows that IAHP is a simple，practical，scientific and effective method． At the same time，the study will provide a reference for other construction projects in evaluating the environmental factors．