In order to explore the impact of planting density on the locust growth, understory vegetation and soil moisture on the Hillygullied Loess Plateau in northern Shaanxi, we observed and analyzed the locust woodland planted around 2 000 with five different planting densities. The results show that: (1) in sunny aspect, the average DBH, tree height and crown between different densities were significantly different(P<0.05). In shady aspect the average DBH and tree height in the density of 2 500 plants/hm² were significantly different from the another two lower densities. The average crown was significantly different from 1 670 plants/hm² while insignificantly from 2 000 plants/hm²(P>0.05).(2) Woodland soil moisture, cover of understory vegetation and species diversity were relatively higher under the density of 1 670 plants/hm². (3) Soil moisture in 0~500 cm depth of locust woodland with each density was lower than that of stable soil moisture (12%) in the study area. （4） In sunny aspect, soil moisture in 0~500 cm depth with density of 3 330 plants/hm² was only 4.5%, while the density of 830 plants/hm² reached 7.8%, and the soil moisture with density of 1 670 plants/hm² and 2 000 plants/hm² was relatively higher in shady aspect, which was 7.5%~8.2%. The study suggests that the initial planting density of locust should not be more than 1 670 plants/hm² (spacing of 2 m×3 m) in the hillygullied loess area and thinning management should be taken to adjust the stand density after entering the peak growth period in order to maintain the stability and sustainability of locust plantation.