Abstract: Taking Pinus massoniana plantations with different forest ages (8 a, 20 a, 32 a, 50 a) as the research object, the soil total nitrogen and available nitrogen contents in different forest ages, soil layers and different months were compared and analyzed. The results showed that: (1) Soil total nitrogen and available nitrogen content increased with the age of Pinus massoniana plantation; (2) Soil total nitrogen and available nitrogen cotent decreased with the increase of soil depth; (3) In one growth cycle of Pinus massoniana plantation, soil total nitrogen and available nitrogen content were different among different age groups in different months, and generally showed a rising-falling-rising trend, which increased with the increase of soil temperature and water content.