Based on the measured salinity at the upper and lower water gate of Qingcaosha reservoir from January to Match from 2015 to 2017, and combined the measured river discharge at Datong station, wind at weather station at Chongming eastern shoal, water level at Baozhen hydrologic station and salinity at Chongxi hydrologic station, the frequency and source of saltwater intrusion at the water intake of Qingcaosha reservoir in the last three years were analyzed. The frequencies at the water intake of the reservoir from January to March in 2015, 2016 and 2017 were three, one and one of saltwater intrusion, respectively. Only one time of saltwater intrusion in the dry season of 2016 and 2017 occurred due to the higher river discharge. Among the total five times of saltwater intrusion happened at the water intake from January to March in the last three years, only one of saltwater source was from upstream, i.e., the saltwater-spilling-over from the North Branch into the South Branch, which took about 3 days for the saltwater moving from the Chongxi hydrologic station to the water intake of the reservoir; Four times of saltwater source were from downstream, i.e., the saltwater intrusion through the North Channel, which appeared in neap tide or medium tide after neap tide, was weaker under general wind speed, and was stronger under strong north wind. In view of the saltwater intrusion at the water intake of Qingcaosha reservoir in the last three years, the frequencies of saltwater intrusion coming from the downstream of the North Channel were increased distinctly, and the saltwater intrusion would be severe if strong north wind occurs in neap tide.