 Some controversies on the forest hydrology were analyzed in this article． The controversies focus on(a)Can forests increase rainfall﹖(b)Can forests decrease annual runoff and regulate flows﹖(c）Can forests reduce floods﹖Many evidences and several viewpoints were listed．By the author＇s point， the effects of forests on precipitation are relatively small forests can reduce annual runoff compared with shorter vegetations and the effects of forest on dry season flow and peak flood mitigation can＇t be made the last word．The reasons that various and contradictive conclusions exist are due to the limitations of research methodology，the complexity of research object and the difference of region and scale． So， the difference of zonality，scale and species or type of forest should be considered when the effects of forest hydrology be evaluated．