Based on the data of conventional meteorological observation, precipitation weather phenomenon instrument, NOAA (National Oceanic and Atmospheric Administration), and ECMWF (European Centre for Medium-Range Weather Forecasts) Reanalysis v5 (ERA5), the upper-level synoptic situations, air-sea temperature difference, low-level shear lines, and atmospheric hydrometeors of the heavy sea-effect snowstorm in December 2023 and the continuous sea-effect heavy snowfall in December 2005 over Shandong Peninsula are comprehensively analyzed. The results are shown below. (1) The strong meridional ridge in Eurasia and the cold vortex circulation in front of the ridge are the large-scale circulation background of sea-effect snowstorm. The broad and stable ridge is the main reason for the long duration of the strong sea-effect snowfall in 2005. The meridional characteristics of ridge and cold vortex are more significant in 2023, so the cold air is stronger. (2) The SST (sea surface temperature) of the Bohai Sea in 2005 and 2023 is higher than that in the normal years. In 2023, the range of temperature 2.5 ℃ higher than the normal years is wider, and the air-sea temperature difference exceeds 30 ℃ from 21 to 22 December. (3) When a snowstorm occurs, there is wind field convergence between westerly and northerly-northeasterly in the north of Shandong Peninsula; the snowstorm at Rongcheng station requires stronger steering flow in the low level. (4) The cloud body is mainly composed of ice crystals and snow crystals, and more snow crystals above the updraft overlap with ice particles from 20 to 21 December 2023, which indicates that the aggregation of snow-ice crystals contributes to the growth of snow particles besides water vapor deposition. The dendritic snow particles produced by the aggregation are conductive to the increase of snow depth. The raindrop size distribution at Wendeng station also shows that the diameter of the snow particles is larger from 21 to 22 December.