Abstract: This study focuses on the extreme rainstorm event in Beijing from 29 July to 1 August 2023. Using ERA5 reanalysis data and surface observations, it investigates the formation mechanism of the low-level jet during this event. The results show that the strong geopotential gradient jointly established by the remnant vortex of Typhoon Doksuri, the mid–high-latitude blocking high, and the subtropical high was the key driver of the low-level jet. The work done by this strong geopotential gradient, together with horizontal advection, triggered the rapid intensification of the jet in its early stage. In the later stage, it became the key energy source that overcame the strong near-surface frictional dissipation and maintained the high kinetic energy of the low-level jet.By decomposing the horizontal kinetic energy advection term, this study further reveals that the remnant vortex of Typhoon Doksuri modulated the dynamic structure of the low-level jet by inducing pronounced anomalies in physical quantities such as divergence, shear deformation, and stretching deformation. The strong convergence and shear deformation anomalies associated with the remnant vortex played a crucial role in the local accumulation and transport of kinetic energy within the jet region. In addition, the warm advection induced by the typhoon remnant vortex and the intense latent heat release from condensation in the rainstorm area were the fundamental causes of the development of the mid–low pressure and mid–high pressure systems, which in turn produced the strong geopotential gradient.