[Objective] The objective of this study is to reveal the development of erosion gully in a typical small watershed in the northern slope of Tianshan Mountains, in order to provide a scientific basis for early warning and control of gully erosion. [Methods] This paper selected 10 erosion gullies in the northern slope of Tianshan Mountains, field survey and GIS technology was used to investigate the characteristics and morphological formation of erosion gully. [Results] (1) There was a significantly positive correlation between the cross section area and the average width and the depth of the gully. Gully area was positively related to the length of gully. Significant positive correlations existed between gully volume and cross-sectional area, and between gully volume and gully area. No significant correlations were found among gully length, average width of gully and the mean depth. Similarly, no obvious correlation existed between catchment area and characteristic value. (2) Erosion gullies in the study area were all open-type and weak erosion type. (3) Gully density was positively correlated with the slope, as greater the gully density tended to occur at the steeper slope. However, there was no correlation existed between gully density and gully length. Gully density was the largest in the southern slope, while in the west and southwest slope, the gully density was relatively small. [Conclusion] The slope and aspect are important geomorphological factors influencing gully development at small watershed scale.