Abstract: In order to illustrate the relationship between forest litter cumulants and its key impact factors, the litter accumulation amount and its main environmental factors of three forest communities(middle-aged Populus davidiana-Betula platyphylla-Picea wilosonii forest, middle-aged Picea wilsonii forest and pre-matured P. wilsonii forest)during the succession of Populus davidiana-B. platyphylla-Picea wilosonii forest were studied by using the methods of spatial series representing temporal series and standard sample survey method in 2013-2014 in Xinglong Mountain of Gansu Province. The results showed as follows:1. The thickness and total accumulation amount of litters decreased at first and then increased with the positive succession of forest communities. The average values of thickness for the three forest communities were 5.26 cm, 5.03 cm and 5.59 cm respectively,and the average values of total accumulation amount were 57.08 t·hm-2, 51.44 t·hm-2, and 56.34 t·hm-2. 2. For the pre-matured P. wilsonii forest, the total accumulation amount of litter was gradually increasing with the increase of elevation, and the average values of the three elevations of 2300 m, 2400 m, 2500 m were 48.56 t·hm-2,55.93 t·hm-2, and 64.55 t·hm-2 respectively;For the middle-aged P. wilsonii forest, the total accumulation amount of litter of high density stand and small slope were greater, but the impact of the density and slope on the acumulation amount of litter was not obvious, the average values for the stand densities of 2133 plants·hm-2, 1705 plants·hm-2 and 1065 plants·hm-2 were 49.87 t·hm-2, 48.59 t·hm-2 and 45.36 t·hm-2 respectively,while the average values for the slopes of 22°, 32° and 41° were 58.35 t·hm-2, 49.9 t·hm-2 and 48.59 t·hm-2. 3. The correlation analysis showed that there was a significant correlation among the accumulation amount of litter un-decomposed and DBH, height, conifer density. The enviromental factors affacting the accumulation amount of forest litter were various, and the litter amount was the result of combined action of many factors.