With the three-dimensional mathematical model, namely, H=exp(a+bx+cx2+dy+ey2),the vertical distribution laws of natural belts in the southeastern part of the Qinghai-Tibet Plateau are studied in this paper. The warmth index (WI) and cold index (CI) of the upper limits of the evergreen broad-leaf forest, the coniferous and broad-leaf mixed forest, the montana dark coniferous forest, and the alpine shrub and meadow belt are 65℃ · month,43℃· month, 16℃· month and 10℃·month, and -10℃·month, -24℃· month,-55℃ month and -75℃· month respectively. The potential evaporation values of them are 620mm, 500mm, 410mm and 300mm respectively.