In order to understand the temporal and spatial changes of the water quality of Alternanthera philoxeroides invaded the Caohai Wetland in Weining, in January 2018 (winter), April 2018 (spring), July 2018 (summer) and October 2018 (autumn), In the Caohai Wetland Alternanthera philoxeroides invasion site, water samples were collected according to the invasion status of Alternanthera philoxeroides to determine pH, total nitrogen (TN), ammonia nitrogen (NH4+-N), total phosphorus (TP), and permanganate index ( CODMn) and chlorophyll a (Chl.a) and other water quality indicators, to analyze the eutrophication status of the water body in the invasion site of Alternanthera philoxeroides and the temporal and spatial changes of water quality. The results showed that: (1) The water quality of Alternanthera philoxeroides in the Caohai Wetland had significant seasonal differences in pH, TN, NH4+-N, TP, CODMn, and Chl.a (p<0.05); TN, NH4+-N, TP, CODMn and Chl.a showed a decreasing trend from upstream to downstream with the changes of waters. TN, NH4+-N, TP, Chl.a showed a significant decreasing trend with the increase of invasion degree (p<0.05); (2)Seasonal changes showed a downward trend, with the worst water quality in spring; the comprehensive nutrient index showed a downward trend along the upstream to downstream with the changes in the water area, and the upstream water quality was the worst; the Caohai Wetland Alternanthera philoxeroides invaded the site water body in an overall moderate eutrophication state; (3) The Caohai Wetland Alternanthera philoxeroides is a phosphorus-restricted area, and restricting the input of phosphorus can effectively reduce the eutrophication of the water body.