The responses to light and CO2 of slash pine’s halfsib were studied for establishing reasonable strategy in heredity improvement and planting using LI-6400 portable photosynthetic system. There were significant differences of the character parameters which responded to light and CO2 of slash pine’s halfsib. The apparent quantum yield on March to April of 1 year needle of slash pine’s halfsib and the apparent quantum yield on April of 2 year needle of slash pine’s halfsib was the highest in a year. The apparent quantum yield on May of 1 and 2 year needle of slash pine’s halfsib was the lowest. The carboxylation efficiency on May of 1 and 2 year needle of slash pine’s halfsib was the lowest while the carboxylation efficiency on August to September of 1 and 2 year needle of slash pine’s halfsib was the highest.The apparent quantum yield and carboxylation efficiency of slash pine’s halfsib were higher than that of general variety. The apparent quantum yield and carboxylation efficiency of 1 year needle were higher than that of 2 year needle’s. The main physiological mechanism of fast growth and high yield of slash pine’s halfsib was that it had highest apparent quantum yield, carboxylation efficiency, saturation point of light, saturation point of CO2 and lower compensation point of light , compensation point of CO2.