Abstract: Existing theories of river confluences have effectively explained fundamental hydrodynamic structures, such as shear layers, flow-separation zones, and stagnation zones, as well as their associated local scour and deposition effects. However, they remain insufficient for interpreting the formation mechanism of long-term active-channel contraction at seasonal river confluences in arid regions. Taking the Kuoshilash confluence of the Hotan River as a case study, this study used Landsat remote sensing images from 1989 to 2020 and gauged runoff records to investigate the staged channel contraction of an arid-region confluence under the combined influence of runoff variation, hydraulic engineering regulation, internal flow-zone reorganization, and sandbar stabilization. The results show that the Hotan River confluence did not undergo continuous channel widening during the study period, but instead exhibited staged contraction. The median bankfull width of the main channel decreased from 1588.5 m to 1324.0 m, with an average narrowing of approximately 267 m. Channel braiding intensity was generally affected by runoff fluctuations, although the response differed between the two tributaries. The coefficient of determination between the total channel index and runoff was 0.6768 for the Karakash River and 0.3042 for the Yurungkash River. From 1989 to 2020, the confluence angle mainly fluctuated between 84° and 95°, indicating that the planform configuration of the confluence remained relatively stable and that its geomorphic response was not primarily characterized by substantial migration of the confluence point. As the flow ratio decreased from 1.257 to 0.806, the shear layer shifted laterally by approximately 678 m toward the tributary side. The staged contraction of the Hotan River confluence represents a geomorphic response to the combined effects of external hydro-sedimentary changes and internal flow-zone reorganization. The key process is that runoff variation and engineering regulation alter the relative hydraulic conditions of the two tributaries, while shear-layer migration and reorganization of low-velocity depositional space affect zonal sandbar preservation. Subsequent sandbar exposure and stabilization further constrict the active channel. These findings provide a reference for identifying confluence-related geomorphic evolution in arid-region rivers and for assessing downstream channel responses to hydraulic engineering regulation.