Investigating a paleoearthquake in a region can be used to study the seismicity of fault zones, and provides guidance for earthquake prevention and disaster reduction in nearby cities. However, the short of reliable records brings challenges to the assessment of the paleoearthquake disasters. With the development of computational seismology, we can study paleoearthquakes using numerical modeling based on limited data, to provide a reference for understanding the physical laws of historical earthquakes and earthquake relief in present society. Taking the 1679 M 8.0 Sanhe–Pinggu earthquake as an example, we built a dynamic model with good consistency between the surface slip and historical records, calculated the strong ground motion based on it, and obtained the intensity distribution that was consistent with the previous investigation. We found that the heterogeneous dip‐slip distribution caused by the fault geometry change may be the reason that the fault scarp only remains about 10 km. In addition, the intensity of Tongzhou area in this earthquake may be as high as XI. In the future, it may be necessary to pay attention to strengthening earthquake prevention and disaster reduction in this area. Then, we estimated the number of deaths in the study area at that time, and the mathematical expectation was of about 74,968. During the systematic retrospective study of paleoearthquakes, as shown in this article, we can gain new understandings of the rupture process of paleoearthquakes and evaluate earthquake disasters more accurately.