Based on the conventional observational data, NCEP reanalysis data and automatic weather station data, the marine effect snowstorm which happened in the west of Laizhou Bay on 8 December 2011 was analyzed diagnostically. The findings show that snowfall occurs in appropriate ambient field, favorable air sea temperature difference and more intensive cold advection. However, differences exist in wind field configuration, air sea temperature difference range, water vapor distribution dynamic conditions and thermal conditions. During this snowfall process, northwest winds blow above 900 hPa whice under the level, it maintains sustained northeasterly which is the main reason for this marine effect snowstorm process. This wind field is different from the northern peninsula where northwest winds blow in both upper and low airs. By analyzing the physical field, the marine effect snowfall belongs to shallow convective snowfall. There is upward motion, moisture convergence center, unstable stratification and large air sea temperature difference under 900 hPa in the west of Laizhou Bay, and the shear line of near surface triggers the release of unstable energy in the process. The heavy snowfall area is the warm tongue of equivalent potential temperature at 1000 hPa. The position of warm tongue here is different from that in the north of Shandong Peninsula. The former is in Laizhou Bay, while the latter is in the northern coast of the peninsula. From the cloud images, the cold airflow clouds on the sea show a streamwise cloud line, and the cloud is individual cells. When nearing the land, the clouds get thickened, cloud line deflects and the intensity of snowfall increases.