Taking Pinus tabulaeformis with different ages in Liao River source region of northern Hebei as study objects, the variations of MBC, MR and q CO₂ were studied. The results showed that with the incrase of forest age, MBC increased gradually, MR decreased first and then increased, soil microbial metabolic quotient decreased. Both MBC and MR had extremely significant negative linear correlation with q CO₂, MBC and MR had an extremely significant positive correlation, while the linear correlation was weaker. Both MBC and MR had extremely significant positive correlation with soil temperature and water content, q CO₂ had extremely significant negative correlation with soil temperature and water content. These results demonstrated that MBC, MR and q CO₂ was closely related to forest age. With the increasing age of Pinus tabulaeformis, soil microbial activity was enhanced and the efficiency of carbolic metabolism increased, which give the soil a higher quality and a greater potential of sustainable use and a more stable ecosystem.