Abstract: In January 2020, a long-term and high-intensity heavy PM_2.5 pollution event occurred in Shizuishan City, typical industrial city, in Ningxia Hui Autonomous Region. This study analyzed the daily air quality index (AQI) and conventional pollutant concentration during the key pollution period from 1^st to 17^th of this event. Then the comprehensive effect of multiple factors on this heavy pollution event was revealed by using the data of environmental air quality, meteorological elements, and NCEP reanalysis and combining the method of statistical analysis, pollution characteristic radar chart, backward trajectory clustering, and weather diagnosis. The results show that: (1) The heavy pollution weather from January 1^st and 3^rd, 2020 was mainly affected by high intensity pollution emissions from coal, industry (steel, coking) and motor vehicles. PM_2.5 mainly came from primary sources. In addition to the local dust, the PM_2.5 on the 9^th was mainly caused by secondary particles. The peak values of ρ(PM_2.5) and AQI were 216 μg/m³ and 266, respectively. Heavy pollution in other periods was caused by the accumulation and mixing of pollutants. (2) Another important factor contributing to the event was the trans-regional transmission of polluted air masses from Wuhai City and its neighboring. When the wind speed of Bayannaoer City-Wuhai City-Shizuishan City was uniformly northerly and less than 2 m/s, the polluted air masses Wuhai City and its surrounding diffused to the south, resulting in a short-term explosive growth of ρ(PM_2.5) in Shizuishan City. (3) The continuous high humidity and static weather conditions maintained and enhanced the pollution process. When the weak zonal westerly wind prevailed in the Eurasian continent at 500 hPa, Shizuishan City was controlled by the bottom average pressure field of the weak Mongolia high, and the wind direction was weak northerly or easterly, which was easy to form continuous PM_2.5 polluted weather. As the wind speed decreased to 0.7 m/s and the relative humidity increased to 78%, the pollution became more serious. In conclusion, the continuous heavy pollution process was the combined and superimposed result of local high-intensity pollution emission, secondary particulate matter generation, regional transmission, and adverse meteorological conditions. When there are unfavorable weather conditions such as static stability and high humidity, it is necessary to strengthen the control of the discharge of various pollutants. At the same time, make full use of the encrypted automatic weather observation data in Shizuishan City and its surrounding areas, study and judge the development trend and transmission characteristics of pollution, and carry out joint prevention and control of air pollution with Wuhai City and its surrounding areas in a timely manner.