Abstract: A backflow heavy snowfall event occurred in central North China from 07:00 BT 5 January to 04:00 BT 6 January 2020, producing a maximum snowfall of 15.5 mm. The ERA5 reanalysis and high-resolution observation data from multiple sources are utilized to analyze synoptic background and local dynamic and thermal conditions of this event as well as the spatiotemporal distribution and microphysical features of snowfall. The results show that 7 h prior to the snowfall, northeasterlies below 900 hPa (called 'backflow') swept the northeast plain of China and the Bohai Sea and reached the North China Plain, under the joint influence of an inverted trough over the Yellow River bend and a high pressure in the Northeast plain. A shallow near-surface mesoscale convergence line formed in the North China Plain under the blocking effect of Taihang mountain. The convergence line corresponds to the heavy snowfall area. At 850 hPa, southeasterly flows around the Southwest Vortex prevailed over the snowstorm area. Northeasterly winds below 800 m were observed in Shijiazhuang about 1 h before the snowfall, and temperature below 1 km height dropped rapidly to −5—−1℃, forming a "cold pad". An Low-Level Jet (LLJ) near 700 hPa over the heavy snowfall area appeared 2 h prior to the snowfall, and the LLJ became thicker and extended down to 2 km. The warm and moist air below the LLJ was forced to climb along the "cold pad", triggering snowfall. The maximum wind speed of LLJ (19 m/s) and the peak value of LLJ index (about 8) coincide with occurrence of the heavy snowfall greater than 1 mm/h. At the same time, the maximum center of ascending motion and water vapor transport is located near 700 hPa. Snow particles are 0.35—0.55 mm in diameter. There is a positive linear correlation between snow intensity and particle number concentration. The snow-producing cloud layer is located at 1.3—5.5 km height. The lower layer (below 3 km; about −10℃) is ice-snow mixing layer and the upper layer (3—5.5 km) is ice-snow layer. Relative humidity in the ice-snow layer is positively correlated with snow particle concentration and snowfall intensity. The fitting relationship between ground reflectivity factor (Z) and snowfall intensity (R) detected by disdrometer is Z=149.85R^1.14. These results provide a reference for better forecasting of heavy snowfall in North China.