The measurements of soil surface moisture characteristics under Platycladus orientalis plantations with 4 different afforestation ages (4, 7, 10 and 13 years) were studied in northern mountain region of Lanhzou. The results showed that: The water conservation contents of Platycladus orientalis forestland varied significantly in different stand ages. The water conservation contents of 4 different afforestation ages increased by 201、268、251 and 208 t/hm2 than that of slope wasteland respectively. Maximum moisture capacity, capillary water capacity, field water capacity and optimal-water-content all increased with the afforestation age. Soil water of 0 ~ 30 cm layer in 4 years of forestland was moderate available, but was hard available for other forestlands. Compared with the wasted land, to some degree, soil moisture content of different plantation stages all increased, and it proved that Platycladus orientalis plantations could improve soil surface water condition.