To study the impact of rainfall and water level changes on the stability of drainage channel slopes, a numerical model was established using a finite element software, incorporating hydrogeological data and on-site sampling test results from the Fengmen River in Lucheng District, Wenzhou. The research findings indicate that the influence of rainfall on the slope’s seepage field primarily depends on the duration rather than the type of rainfall when there are adjacent buildings and the soil permeability of the slope is relatively low. Throughout the process, significant seepage did not occur in the slope. The water level in the channel and the adjacent buildings are the main factors affecting the stability of the slope. Higher water levels contribute to higher slope stability, while closer proximity of buildings to the channel and larger loads have a negative effect on the stability. Although the dense distribution of buildings may decrease slope stability, it also reduces the sensitivity of slope stability to changes in water levels. In all operating conditions, the stable safety factor of the drainage channel slope is larger than the critical stable safety factor(1.20). This indicates that the current slope of the bank is in a safe state and no additional support measures are necessary.