The Life Cycle Assessment (LCA) method was used to compare and study the environmental impact of the whole production process of P·O 42.5R cement and P·Ⅱ 42.5R cement produced before and after the use of mixed material in a cement plant in Guangzhou, and the evaluation results were analyzed. Six environmental impact types were selected: Global Warming Potential(GWP), Acidification Potential(AP), Abiotic Depletion Potential(ADP), Eutrophication Potential(EP), Respirable Inorganic material(RI), and Photochemical Ozone Formation Potential(POFP). LCA calculation shows that adding 3.34% gangue and 3.32% fly ash in the cement grinding process can reduce the six environmental impacts of the cement production process. GWP, ADP, AP, EP, RI and POFP decreased by 8.52%, 9.18%, 9.09%, 8.68%, 8.88% and 8.29% respectively.