Based on comprehensive observation data, the basic characteristics of 31 Bohai ocean-effect rain events in autumn from 1999 to 2020 are statistically analyzed, and the formation mechanism of ocean-effect rain is revealed through the analysis of typical ocean-effect rain events. Moreover, the comparative analysis on Bohai ocean-effect rain and ocean-effect snow is conducted. The results are as follows. (1) Bohai ocean-effect rain in autumn usually occurs between mid-October and November, with the highest frequency in early-to-mid November. Only rain occurs in October while rain, sleet, or snow is possible in November. Bohai ocean-effect rain events are distributed in the northern coastal areas of Shandong Peninsula, and the rainfall during the event is light rain, which lasts no more than 1 d. (2) The intensity of cold air during ocean-effect rain is weaker than that during ocean-effect snow. During rain, the temperature at 850 hPa over Shandong Peninsula is about -1 ℃ in October and -6 ℃ in November. When rain turns to sleet or snow in November, the temperature at 850 hPa is generally between -9 and -8 ℃, and the surface temperature is between 2 and 4 ℃. (3) The circulation pattern of typical Bohai ocean-effect rain event is manifested as cold vortex at 500 hPa, northwest cold advection at 850 hPa, and cold high pressure system at surface. Strong cold air invades Bohai and Shandong Peninsula, causing shallow convective instability in the northern coastal areas below 790 hPa, and the convergence of wind direction and speed triggers unstable energy to produce ocean-effect rain. During the period of heavy ocean-effect rain, there is a shear line between northeast wind and northwest wind in the lower troposphere in the northern coastal areas, and the wind speed convergence is obvious. The maximum radar reflectivity is between 45 and 50 dBZ. (4) The characteristics of circulation pattern, water vapor source, thermal conditions, dynamic conditions, and radar radial velocity of Bohai ocean-effect rain are basically the same as those of ocean-effect snow, but the main differences lie in sea surface temperature and intensity of cold air. The critical period for forecasting Bohai ocean-effect rain is from late October to November.