The low-frequency energy spectrum of the coastal water level of the Bohai Sea is analyzed, the main frequencies for the peaks of the energy spectrum density being 1/5 cycle/day and 1/3 cycle/day. Also analyzed are the coherence, the variation of phase angle and the system functions among the stations. Finally, a discussion is made on the relationship between the forcing and the water level change, thus coming to a conclusion that the low-frequency change in the water level is mainly due to the energy supplied by wind stress. The low-frequency energy spectrum of the coastal water level of the Bohai Sea is analyzed, the main frequencies for the peaks of the energy spectrum density being 1/5 cycle / day and 1/3 cycle / day. Also analyzed in the coherence, the variation of phase angle and the system functions among the stations. Finally, a discussion is made on the relationship between the forcing and the water level change, thus coming to a conclusion that the low-frequency change in the water level is mainly due to the energy supplied by wind stress.