A Yellow River cyclone rainstorm event occurred in Shandong from 8 to 9 August 2025, while both subjective and objective forecasts predicted the rainstorm area to be more northward. This study analyzes the large-scale circulation background, the triggering of mesoscale convective systems, the developing mechanism of Yellow River cyclone and the possible causes of forecast deviation based on multi-source observational data, ERA5 reanalysis data and forecast data of various numerical models. The results are shown below. (1) This event occurs in a background where the western Pacific subtropical high presents a zonal distribution, the northeast cold vortex and the trough on its south side lie northward, the northwest airflow prevails in the middle level over Shandong, and a Yellow River cyclone moves eastward, affecting most areas of Shandong in the lower level. During the event, the water vapor in the Huang-Huai region is abnormally strong with moderate unstable conditions, which exhibits a high potential for convective heavy precipitation. (2) The main reasons for the precipitation deviation are the northward forecast of the location of Yellow River cyclone and the weak terrain precipitation forecast in the mountainous areas of central Shandong. (3) In future forecasts, a comprehensive analysis of the occurrence and development mechanism of surface cyclones should be conducted. When the upper-level systems are not significant, the analysis of lower-level systems should be more comprehensive, especially the role of cold pools caused by sea-land breeze circulations, the terrain of Taihang Mountains and convective precipitation, which needs to be given special attention. The amplification effect of the mountainous areas of central Shandong on the rainstorm event lies in the action of circumfluence under the background of weak circulation and the convection triggering and organization on the south side of Mountain Tai under strong southerly airflow. When a southeasterly jet exists in the super-low level, turns clockwise into a southwesterly low-level jet, and decreases slightly with the increase of height, special attention should also be paid on the increase of precipitation on the south and east sides of Mountain Tai.