To understand the seasonal variation of plant organs-litter-soil stoichiometry in Pinus tabulaeformis plantation in Loess Hilly region, the field investigation and laboratory experiments were used by means of spatio-temporal substitution method in Zhifanggou Watershed, Ansai District, Yan'an City, Shaanxi Province, China. The ecological stoichiometry characteristics of carbon (C), nitrogen (N) and phosphorus (P) in different organs-litter-soil of Pinus tabulaeformis from April to October were analyzed. The results showed that:(1) From April to October, the contents of C and P in leaves increased gradually, and reached the highest in October. The contents of N and N:P in leaves and branches decreased first and then increased, and reached the lowest in August. While the contents ofC:N and C:P in branches and C:P and N:P in fine roots increased first and then decreased, and reached the highest in August. Soil C and N contents, C:P and N:P increased first and then decreased, and reached the highest value in August. Litter N content, C:P and N:P all showed a trend of decreasing first and then increasing, and reached the lowest in June, while P content had no significant change. (2) Except for N:P>14 in leaves from April to June and fine roots from April to August, N:P<14 in other organs from April to October, the growth of Pinus tabulaeflorus in this region was mainly restricted by N. (3) There were significant positive correlations between C and N contents and C:N of leaf and litter, and there were significant positive correlations between C:N, C:P and N:P (p<0.05). There was a significant negative correlation between leaf N:P and soil C:N (p<0.01), but no significant correlation between other stoichiometric characteristics. There was a significant positive correlation between litter C content and soil P content (p<0.05). The results make the study of ecological stoichiometry of plantation more systematic and provide reference for vegetation growth in loess hilly region.