The Qingnian ship lock is the lowest cascade of the Pinglu Canal.After the construction of Pinglu Canal,the salt water intrudes from the Maowei Sea to the downstream approach channel of the Qingnian ship lock.The Qingnian ship lock is characterized by a salt-fresh water confluence water environment.With the operation of the Qingnian ship lock,salt water will intrude into Qingnian reservoir.Because of the unfavorable impacts of salt water intrusion,it is necessary to study the salt water intrusion at Qingnian reservoir which serves as the source of water for domestic drinking and agricultural irrigation of Qinzhou City.By constructing a three-dimensional numerical model of salt water intrusion of Qingnian reservoir,the effects of fresh water discharge and the salinity of the upstream approach channel of Qingnian ship lock on the distance of salt water intrusion and the vertical salinity distribution are studied.The results show that the salt water intrusion distance increases with the increase of water salinity at the upstream approach channel,showing a positive power relationship,and decreases with the increase of fresh water discharge,showing a negative power relationship.The vertical salinity gradient decreases with the increase of water salinity at the approach channel,showing a negative power relationship,and increases with the increase of fresh water discharge,showing a positive power relationship.