Abstract: Forest gap size and plant metering chemical coupling relationship are the basis of forest management, and Pinus massoniana plantation in related research is still lacking. Our research object is located in Yibin County town of 41-year P.massoniana plantation. Weset up eightdifferent size forest gaps(CK:0 m², G1:100 m², G2:225 m², G3:400 m², G4:625 m², G5:900 m², G6:1 225 m² and G7:1 600 m²), and through the investigation, selected natural update herb Dicranopteris dichotoma, Miscanthus sinensis and Setaria plicata on leaf N, P stoichiometric features to explore. Advantage herb average N content in the study area was 15.25 mg·g^-1, the average of P content was 1.19 mg·g^-1,and the update plant was mainly restricted elements of N elements. With the increase of forest gap area, the forest light intensity, temperature and humidity were significantly increased. Advantage herb leaf N, P content is affected by forest gap size significantly, P content was increased with forest gap area of each species with a trend of decrease. N content in different species change with forest gap size wasdifferent, the rule of D.dichotoma N content was increased with forest gap area and dropped significantly. M.sinensis and S.plicata were increased with the increasing of forest gap area of N content significantly. On the leaf N, P stoichiometric level, the optimal gap covers of D.dichotoma was 100-225 m², and the optimum forest gap covers of M.sinensis and S.plicata was 1 225-1 600 m². The above results show that by nearly natural transformation,forest tending and other measurescan promote the artificial forest nutrient cycling and improve P.massoniana artificial forest ecosystem productivity.