Abstract: With the three-dimensional development of modern urban space, the three-dimensional urban form has become an important factor that affects the surface thermal environment.Current research predominantly focuses on the evolution and impacts of the surface thermal environment in 2D urban morphology, while studies and considerations of 3D urban morphology remain limited, with this issue being particularly pronounced in valley-type cities.Thus, this study focuses on the impacts of 3D urban morphology on the surface thermal environment in the downtown area of Lanzhou city, based on Landsat 8 OLI satellite remote sensing data, building silhouette data, and other datasets, coupled with the optimal parameter geographical detector（OPGD） and multiscale geographically weighted regression（MGWR） model.The study aims to provide references for rational urban planning, improving urban thermal environments, and enhancing urban livability.The results show thatin the 3D urban morphology, the sky view factor（SVF） and high building proportion（HBP） are the dominant factors influencing land surface temperature（LST）.SVF’s differing effects on ventilation and solar radiation reception result in both positive and negative impacts on LST.The positive impacts decrease from the center of Chengguan district outward, whereas the negative impacts show a diminishing trend from the center of Xigu district.An increase in HBP facilitates the mitigation of the urban heat environment.The interactions between various 3D morphology factors and NDBBI provide stronger explanatory power compared to individual factors.