Abstract: To reveal the regression effect between the sapling increment and the rate of P application, an experiment of phosphorus fertilizer was conducted in 3a low-yield young Cunninghamia lanceolata forest. The conclusions have been showed as follows: a parabolic trend equation was efficiently affected the relationship between the increment and the application amount, which showed a typical convex curve and one peak each index of increment reflected. Each index of increment rose with the increase of P fertilizer amount before the crest, and turned to degradation with the increasing of fertilizer application after the peak. According to the results, 0.098kg and 0.100kg per tree of P fertilizers were applied to trees which average height and base diameter was corresponded to the maximum respectively, the greatest height and base diameter in theory were 1.48m and 3.15cm, and respectively increased by 49.5% and 37.6% were compared to the comparison’s.