A research was performed on a series of plots with similar conditions in broad leaved forest and in the first ,the second ,the third generations of Chinese fir to examine the effects of substituting Chinese fir for broad leaved forest and continuous monoculture with Chinese fir at the same site on soil water,soil nutrient.The results indicated that,with the substitution of Chinese fir plantation for broad leaved forest and the increasing of continuous plantations of Chinese fir,the ability of soil water keeping and supply descended,most of the soil total nutrient contents decreased,the ability of soil fertility supplying and keeping declined,which affected the Chinese fir growth directly,It is one of the main reasons for soil degradation at the sites with continuous Chinese fir planting.