An artificial lake is made to  the east low-lying region of Lanzhou city area for the purpose of exploring new air pollution control in Lanzhou City. In this investigation, two set of triple nested experiments which include without  and with the lake experiments were conducted using the mesoscale numerical model RAMS developed by Colorado State University and the MRC / ASTER, and the characteristics of atmospheric boundary layer and lake effect in valley city were simulated. The results are as follows:(1) During the day, the intensity of valley breeze is maximum at 14:00. After making a artificial lake, lake breeze strength increases at 14:00, and the lake breeze has no significant effect on the valley breeze except for the surface of lake and the shore near the lake. During the night, the mountain breeze is emergence after 20:00 at night, around 05:00 the mountain breeze speed of north mountain is greater than south mountain.After 05:00,the mountain breeze speed of south mountain increases. The valley is main the west wind. After making a artificial lake,the lake breeze is obvious around 02:00, and land breeze and mountain breeze overlapping with each other, leading to the eastern part of Lanzhou valley westerly wind speed increased.(2) The temperature around the lake is increased in the winter, and the intensity of increase is weakened with the distance from the lake further away. The intensity of inversion temperature near the lake is lower at night. (3) After making an artificial lake, the air relative humidity is reduced on the nearr surface of the lake. Near the west shore of the lake, the air relative humidity for the first reduced then increases. It is obvious in the evening. the air absolute humidity is increase on the near surface of the lake.(4) The net radiation and sensible heat flux are obviously reduced in the lake area. Near the east and west shore of the lake, the net radiation and sensible heat flux are increased more. In the evening between 22:00 to 05:00, the net radiation and sensible heat also increases at the inland where the distance from the lake is a little far away.