In view of the safety problem caused by river sand mining in Lanzhou section of the Yellow River, we established a comprehensive evaluation index system of the influence of river sand mining from the aspects of river regime stability, flood control safety and water environment safety. An improved G2 method and CRITIC method were adopted to conduct combination weighing towards the evaluation indexes subjectively and objectively. Based on the harmony theory, an evaluation model was established to evaluate the influence of river sand mining in Lanzhou reach of the Yellow River from 2013 to 2018. The results indicate that the river sand mining in Lanzhou reach of the Yellow River is harmful to the safety of the Yellow River and the environment, so it is necessary to control and prevent river sand mining in Lanzhou reach of the Yellow River in a certain period of time, avoiding further damage to the safety of river and environment caused by river sand mining.