Abstract: Using multiple observations from regional automatic weather stations, S-band Doppler weather radar, L-band wind profile radar, and ERA-5 reanalysis data, the characteristics and formation mechanism of a warm-sector heavy rain event during June 2022 in Shandong province are analyzed. The results obtained are as follows. (1) The event occurred against the background of an unstable warm air mass with a substantial enhancement of low-level jets, the westward and northward movement of the Subtropical High and no obvious cold air forcing, with weak baroclinicity and abundant water vapor transport. (2) Development and evolution of the rainstorm convective system can be divided into two stages: the first corresponds to the rapid growth of local convections (daytime of June 26) and the second presents back-building of band-like convections (the night of June 26). Prior to the precipitation, the southwesterly wind under 2000 m gradually strengthened, forming a low-level jet showing good correspondence with the beginning of the first stage of precipitation. After 2000, June 26, the jet stream was significantly strengthened, and its level significantly deepened. A combination of depressions in the outflow area of the jet stream, cyclonic wind shear in the lower level, differential vorticity advection, warm advection, and diabatic heating was conducive to the development of the upwelling movement. A convection instability stratification with high temperature, high humidity and high energy was reconstructed repeatedly due to the warm and wet transport of the low-level jet, which is an important reason for the development and strengthening of the convection. (3) Surface convergence line is the key factor responsible for convective triggering and the gradual organization of a band-like convective system. In particular, during the second stage, the similar direction of the ground convergence line, the low-level jet stream axis, and the movement direction of the radar echo provided favorable conditions for the backward propagation of convection, causing the train effect. (4) Large value area of the ingredient-based propagation index (IPI) shows good correspondence with the propagation of convective generation during two stages, which can effectively indicate the potential of convective development.