Geomorphic evidence from several closed lake basins in Tibetan Plateau indicates that the plateau experienced high lake levels during some episode of the period of 40~30 ka BP, and lakes covered an area of about several or tens times as large as at present. Using the equation of hydrologic and energy balance and the multiapproach method to estimate climate parameters such as albedo, cloudiness and vapor press, to calculate the evaporation, simulating the combined hydrologic and energy balance of Zhacang Caka, Seling Namu Cuo, Zhabuye Caka paleolakes with the water balance model of the whole closed basin, respectively, yield the estimates of 475±25 mm/a, 585±25 mm/a, 565±25 mm/a of annual precipitation during 40~30 ka BP at high lake levels period, the estimates of annual evaporation from lake surfaces 1 126 mm/a, 1 044 mm/a and 1 071 mm/a, and from land basins 384 mm/a, 423 mm/a, 422 mm/a, respectively. The amount of increased precipitation at that time must have been about 300 mm/a(71 to 380%) above the modern average. The pattern of precipitation, like the present, is larger in the east part than in the west part of the Tibetan Plateau, which shows the precipitation was triggered by Indian monsoon like the present, but Indian monsoon was far stronger than today.