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Pinus sylvestris var. sylvestriformis is an endemic plant in Changbai Mountain area of China. Five different light levels were simulated and designed with control experiments: full sunlight (CK), light shading (light transmittance was 10%) (LA), light and moderate shading (light transmittance was 20%) (LB), moderate shading (light transmittance was 40%) (LC), and severe shading (light transmittance was 60%) (LD). The optimal light levels and the main physiological and ecological factors affecting photosynthesis in different growth stages were discussed. The results showed that the phenotypic index and photosynthetic physiological and ecological indicators were the highest when the light transmittance was 40%. In the early growth phase, the physiological factors intercellular CO2 concentration (Ci) and ecological factors transmittance (Tran) and air temperature (Temp) jointly affected the changes of net photosynthetic rate (Pn). In the peak growth phase, transpiration rate (Tr), air humidity (RH), and Tran had greater direct positive effects on Pn, and Ci and stomatal conductance (Gs) had direct negative effects on Pn. In the later growth phase, Tr and Ci had large direct positive effects on Pn. The research results could provide important references for the scientific cultivation and popularization of P. sylvestris var. sylvestriformis. [ABSTRACT FROM AUTHOR]