Objective: To investigate the species composition, population density, and seasonal fluctuation of mosquitoes in Huai'an, Jiangsu Province, China from 2018 to 2022, so as to provide a scientific basis for the control of mosquitoes and mosquito-borne infectious diseases. Methods: The adult mosquito density data monitored by lamp trapping method in Huai'an from 2018 to 2022 were collected, and the species composition, population density, and seasonal fluctuation of mosquitoes were analyzed. The mosquito species composition ratio was compared using the Chi-squared test. The mosquito density in different habitats was analyzed using Welch's analysis of variance. Results: Culex pipiens pallens was the dominant mosquito species in Huai'an from 2018 to 2022. The species composition ratio was statistically different between different years (all P < 0.001). Cx. tritaeniorhynchus was the dominant mosquito species in livestock sheds, while Cx. pipiens pallens was the dominant mosquito species in the other habitats, with a statistical difference in the species composition ratio between different habitats (χ²=22 424.835, P < 0.001). Among different habitats, the highest density was in livestock sheds with 3.62 mosquitoes/lamp·h, and the lowest density was in residential areas with 0.92 mosquitoes/lamp·h. Welch's analysis of variance showed that the mosquito density differed statistically between different habitats (F=5.843, P=0.013). The seasonal fluctuation of mosquito density in Huai'an showed a unimodal curve in each year of 2018 to 2022, with the peaks occurring in July for 2019, 2020, and 2022, in August for 2018, and in June for 2021. The seasonal fluctuation of mosquito density showed a single-peak pattern in different habitats and for different species, with the highest densities in July. Conclusions: The species composition and density of mosquitoes differed in different habitats of Huai'an. The highest mosquito density was in livestock sheds, which should be the key area for mosquito control. Mosquitoes were most active during June to September, and mosquito control should be strengthened based on mosquito activity patterns in this period.