Abstract: Through the analysis of fossil diatom in the sediments of Haolaihure ancient lake, which is located in the monsoon fringe area in North China, the environmental evolution has been reconstructed since the Holocene. According to the variations of the diatom assemblages, the environmental evolution of Haolaihure ancient lake since the Holocene has been divided into 6 stages. Ⅰ(12.1-11.5 cal. ka B.P.), the climate was cold; Ⅱ(11.5-8.6 cal. ka B.P.), the temperature increased, but still with cold and hot fluctuation; Ⅲ(8.6-6.7 cal. ka B.P.), the climate was still relatively cool and dry; Ⅳ(6.7-5.8 cal. ka B.P.), the climate began to be warm; Ⅴ(5.8-2.9 cal. ka B.P.), the climate was warm and humid, and it was the Holocene optimum; Ⅵ(2.9-0.2 cal. ka B.P.), the climate trended to be cool and dry, and the lake level decreased gradually and finally dried out at about 0.2 cal. ka B.P..