Background Slope length is one of the important geomorphological factors that affect the process of slope runoff erosion and sediment production. It determines the variation of slope water flow energy along the way, and affects sediment carrying capacity of the water flow, thereby affecting the process of soil erosion, transportation and deposition. In recent years, the research on impact of slope length on soil erosion has received considerable attention. Meanwhile, understanding the changing law of critical slope length provides an important theoretical basis for the study of sediment transport and deposition processes on slopes.

Methods Based on the literature review, we summarized the influence of slope length on runoff erosion and sediment yield, the general law of erosion critical slope length, the calculation method of critical slope length and the influence of slope length on slope deposition. And we discussed the limitations of soil erosion in terms of slope length, and highlighted the focus of future research. The information for the methods comes from 46 core papers out of 2199 papers published in the web of science, CNKI, Baidu Academic and Science Direct in the past few decades with the keywords of "slope length soil erosion" and "slope surface deposition".

Results 1) The relationship between slope length and soil erosion is very complicated. Due to the difference in experimental conditions, the erosion intensity varying with slope length has three dynamic forms: increasing, decreasing and fluctuating. 2) Through previous studies, we summarized the definition of the critical slope length for erosion, and pointed out that different critical slope lengths are obtained in different studies due to factors such as rainfall conditions, slope, and slope length. Moreover, the established calculation model of critical slope length is based on the experimental data of researchers, which causes certain limitations. 3)During the erosion, transportation, and deposition of the slope, the sediment is characterized by alternating strong and weak spatial changes. The existence of the critical slope length makes the influence of slope length on slope erosion and deposition more complicated. When the slope length does not reach the critical slope length, erosion and sedimentation activities cannot be fully developed.4)The key points of future research are described as follows. First of all, it is necessary to carry out further research and experiments on the sediment deposition process on the slope. Second, research on the critical slope length for erosion changes as well as experimental research on the relationship between slope lengths of different soil textures and soil erosion should be strengthened. Finally, slope length affects the wave form of slope erosion-sedimentation, and the coupling mechanism of slope length and slope erosion and sediment deposition process needs to be studied.

Conclusions This paper summarizes the research progress and future research directions of slope length on slope erosion, transportation and deposition process, and aims to provide guidance for the research application and decision-making of soil erosion on slope length.