Abstract: Building upon previous studies of seismic activity in the Sanhe-Pinggu region, this study employs a multi-magnitude, multi-rupture approach to simulate the ground motion of the Sanhe-Pinggu earthquake, with a primary focus on investigating its magnitude. Firstly, historical intensity curves within the study area are transformed into peak ground acceleration （PGA） and peak ground velocity （PGV）. Subsequently, a comparison is drawn between these values and the simulated results under various magnitudes and rupture scenarios. Analyzing the differences, we preliminarily identify three potential magnitudes that closely align with the Sanhe-Pinggu earthquake: M_W7.8, M_W7.9, and M_W8.0. Further, an in-depth comparison is conducted between the 180 rupture patterns associated with these three magnitudes, examining the spatial distribution of intensities and their similarity to historical intensity patterns. Four rupture patterns are selected as the most compatible. By comparing the intensity curves generated by these four patterns to historical data, the true magnitude of the Sanhe-Pinggu earthquake along the Xiadian fault within the region is ultimately determined. The research findings reveal that this magnitude is lower than the commonly acknowledged M_W8.0, trending more towards M_W7.9− or even M_W7.8＋＋.