Abstract: The paper aims to study the physiological responses of Pinus tabulaeformis seedlings to water stress and discuss drought resistance mechanism. In the present investigation, activities of superoxide dismutase (SOD) and polyphenol oxidase (PPO) of Pinus tabulaeformis needles were analyzed and determined. Needles obtained from 3 years seedlings which were planted in the flowerpots. With water controlling, the soil water content of each treatment was established (T1: over 20%; T2: 10.1%-20%; T3: 5.1%-10%; T4: under 5%). The activities of SOD and PPO were determined by colorimetric analysis every 3 days. The results showed that: along with the stress time, the SOD activity increased at first and reached the maximum on the 6th day, then decreased, while there was a rebound phenomenon on the 12th day. Under the same time of drought stress, the SOD activity showed no significant difference among T1, T2 and control group, while those of T3 and T4 were significantly lower than that of the control treatment (P <0.05). The PPO activity increased first then decreased with water stress time. The PPO activity of T1 decreased after 9 days, while that of T2, T3 and T4 decreased after 12 days. It proved that Pinus tabulaeformis had stronger self-repair ability and could repair itself in a short time when the soil water content was over 20%. The PPO activity increased along with the degree of water stress when soil water content was over 10%, while it decreased when soil water content was less than 10%, indicating that enzyme activity decreased when the water stress was excessive.