The mothod for computing the longtcrm land evaporation in China is classified into three kinds in this peper. The first one belongs to a constant relationship. The second one gives a formula in which some parameters represent the effects of geography and climate.The thrid one can only be used in some special regions. Thus, the formula E/r = thD (E₀/r) is suggested to compute the longterm average evaporation in this paper.The suggested formula has been analysed and demonstrated in mathematics and in the concepts of climate and physics, and it is considered to be rational and feasible.This it, checked by a large amount of data in China and other countries meeting the heed of the precision. An analysis on some special climalical and geographical conditions and hydrolog ical effects is made for the parameter D which represents the affecting factor of various climates and underlying surfaces.