Abstract: To study the physiological characteristics under the PEG-6000 simulated drought stress, half-year-old Pinus yunnanensis var. tenuifolia seedlings were planted under 6 different soil moisture levels (CK, 0.5%, 1.0%, 1.5%, 2.0%, 2.5%, 3.0%). The results showed that with the increasing of concentration of PEG-6000 aqueous solution, the survival rates of P.yunnanensis var. tenuifolia seedlings decreased gradually. Activity of APX increased first and then decrease, SOD significantly increased first and then has no obvious change, and they reached the maximum at 2.0% PEG-6000. Activity of PPO was 4.5 times that of CK at 3.0% PEG-6000. When the concentration of PEG-6000 was equal or greater than 1.0%, activity of POD increased positively. MDA, soluble sugar and soluble protein tend to increase, chlorophyll content of leaves of P.yunnanensis var. tenuifolia seedling decreased positively. The findings indicated that P.yunnanensis var. tenuifolia seedlings have the drought resistance to protect itself from drought stress by osmotic adjustment and antioxidant enzyme system.