Korean pine(Pinus koraiensis) and broadleaved mixed forest in Northeast China has been changed regressively into secondary forest with almost no conifers.Planting Korean pine trees under the canopy of secondary forest is a feasible approach for recovering Korean pine and broadleaved mixed forest.For establishing an effective growth promotion method for under-canopy planted young Korean pine trees,two stands were selected as the experiment plots,Stand A(planted in 1989) and Stand B(planted in 1982),and an experiment of microenvironment regulation was conducted relying mainly on Opening degree(K=1,K=1.5,K=2,CK) in 2004.The results were shown that the adjustment had promoted growth of diameter and height of Korean pine planted in Stand A and Stand B,and had a significant influence on the growth rate of basal diameter,diameter at breast height and height in the two growth stands.The four years periodic increment of mean diameter and height of Korean pine planted in 1989 and in 1982 after regulation in K=1 level were 63.4%(D0) and 82.7%(H),64.8%(D1.3) and 69.7%(H) higher than that of control respectively.Quantitative regulation had significant influence on specific leaf area of Korean pine planted in 1989,and the current year specific leaf area(SLA) was lager than perennial year SLA.Quality indexes of natural pruning capacity,normal form quotient and crown size was not significantly changed but shown a positive tendency.The regulation scheme of Opening degree K=1 might be proper for adjusting the microenvironment of Korean pine trees planted under the canopy of secondary forest when the Korean pine trees were in the growth period of 15 to 26 years old in the experiment region. Korean pine (Pinus koraiensis) and broadleaved mixed forest in Northeast China has been changed regressively into secondary forest with almost no conifers. Planting Korean pine trees under the canopy of secondary forest is a feasible approach for recovering Korean pine and broadleaved mixed forest. For establishing an effective growth promotion method for under-canopy planted young Korean pine trees, two stands were selected as the experiment plots, Stand A (planted in 1989) and Stand B (planted in 1982), and an experiment of microenvironment regulation was conducted relying mainly on Opening degree (K = 1, K = 1.5, K = 2, CK) in 2004.The results showed that the promoted promoted growth of diameter and height of Korean pine planted in Stand A and Stand B, and had a significant influence on the growth rate of basal diameter, diameter at breast height and height in the two growth stands.The four years periodic increment of mean diameter and height of Korean pine planted in 1989 and in 1982 after r egulation in K = 1 level were 63.4% (D0) and 82.7% (H), 64.8% (D1.3) and 69.7% (H) higher than that of control respectively. Quantitative regulation had significant influence on specific leaf area of ​​Korean pine planted in 1989, and the current year specific leaf area (SLA) was lager than perennial year SLA.Quality indexes of natural pruning capacity, normal form quotient and crown size was not significantly changed but shown a positive tendency. The regulation scheme of Opening degree K = 1 might be proper for adjusting the microenvironment of Korean pine trees planted under the canopy of secondary forest when the Korean pine trees were in the growth period of 15 to 26 years old in the experiment region.