Several sandstorms occured in northern China in early 2021, especially the rare serious one on March 15. The maximum hourly mean concentrations of PM10 in three sandstorm processes in Beijing reached 7506, 2567, and 1456 mu g/m(3), respectively. The maximum daily mean concentration of PM10 reached 1630 mu g/m(3). Consecutive days of high PM10 concentrations in mid-to-late March led to the monthly mean concentration exceeding 150 mu g/m(3) for the first time since 2017, and it also to be the highest monthly mean concentration in recent years. Air mass transport analysis results showed that the strong uplift of dust particles from desertification areas and the long-range transport of dust particles should be the important reasons for the outbreak of large-scale serious sandstorms. The development and eastward movement of the Mongolian cyclone should be mainly responsible for the sandstorms on March 15 and 28. The desertification in Mongolia should be an important cause of these two serious sandstorms. And the arid areas in northern China might have contributed to the intensification of the sandstorms. The arid areas in southern Mongolia and northern Inner Mongolia might be important sources of dust particles for the sandstorm on April 15.