[Objectives]  To analyze the spatial distribution of Orchestes alni larvae and identify factors useful for forecasting and controlling this pest. [Methods]  The ratio of infested grey elm trees and the population density of the O. alni were quantified in the Helan Mountains. The spatial distribution of O. alni larvae was investigated using six aggregation indices and regression analysis. [Results]  The ratio of infested elm trees in the center of the Helan Mountains was obviously higher than in northern and southern parts. Significantly more larvae were found on semi-shady slopes and more were found on shady slopes than on sunny slopes and valleys. The highest densities were in the lower crowns of grey elm trees, but height and aspect otherwise had no significant effect on abundance. There was a significant positive correlation between larval damage and elm height. Larvae had an aggregated spatial pattern and the basic unit was individual groups. The spatial pattern was density dependent; i.e. aggregation increased with population density. Aggregation was the result of behavior and environmental conditions. The abundance of larvae in grey elm forest was significantly affected by elevation and slope; larvae were mainly concentrated on steep slopes above 1 800 m. [Conclusion]  Mid elevation valleys in the central the Helan Mountains are the key areas for monitoring the occurrence of O. alni larvae. Larval density was higher on sheltered, semi-cloudy slopes with good water. The aggregated distribution of O. alni larvae can easily cause high local densities.