This paper designs a new and scientific environmental quality assessment method, and takes Saihan dam as an example to explore the environmental improvement degree to the local and Beijing areas. AHP method is used to assign values to each weight.7 primary indicators and 21 secondary indicators were used to establish an environmental quality assessment model. The conclusion shows that after the establishment of Saihan dam, the local environmental quality has been improved by 7 times, and the environmental quality in Beijing has been improved by 13%. Then, the future environmental index is predicted. Finally, the Spearson correlation coefficient is analyzed, and it is proved that this method’s correlation is 99%. Finally, the back-propagation algorithm is used to test and prove that the error is little.