On 4 August 2024, heavy rainstorm occurred at Wucheng Station in Dezhou, Shandong Province, breaking the historical records for both daily precipitation and maximum hourly precipitation at the station. Utilizing the observation data from automatic weather stations, Doppler weather radar and wind-profiling radar, as well as ERA5 reanalysis data and GDAS data, combined with the HYSPLIT model, this study reveals the multi-scale physical mechanisms that enabled the long-lasting backward propagating convective system and the extreme precipitation it brought. The results indicate that this event occurred under a large-scale circulation pattern characterized by a rearward-tilted trough confronting the subtropical high. Low level jet (LLJ) and ultra-low-level jet (ULLJ) persistently transported abundant water vapor from the South China Sea and the Bay of Bengal to northwestern Shandong, establishing an extremely unstable environment with high energy, high temperature and high humidity within the warm sector ahead of surface front. The cold pool outflow generated by precipitation interacted with the ambient warm, moist airflow, forming a quasi-stationary convergence line. Coupled with temporal and spatial pulsations of the LLJ, this interaction continuously drove new convective cells to propagate southwestward, directly causing the extreme heavy precipitation. The dynamic reconstruction of energy was the key to maintaining the system. Rainfall consumed unstable energy, but the persistent warm, moist advection transported by ULLJ allowed convective available potential energy to be rapidly rebuilt and maintained at its peak. Thus, a positive feedback self-sustaining mechanism of “energy transport-convection consumption-energy reconstruction” was formed, and it was this mechanism that led to the sustained occurrence of the back-propagating heavy precipitation.