Objective　To analyze the composition, population density, seasonal trends, and insecticide resistance monitoring results of vector mosquitoes in Liaocheng City from 2020 to 2022, providing a reference basis for further mosquito control measures. Methods　According to the "Implementation Plan for National Vector Biomonitoring", adult mosquito monitoring was carried out using mosquito traps and double-layer stacked nets at two national level monitoring points in Dong’e and Chiping. The Bretu Index method was used for monitoring throughout the city, and the immersion method was used for monitoring mosquito insecticide resistance. The monitoring period for adult mosquitoes was from March to November, and for juvenile mosquitoes was from May to October. Results　From 2020 to 2022, a total of 816 mosquito traps were deployed, capturing 4 717 adult mosquitoes with an average density of 5.78 mosquitoes per trap-night. Among them, 4 232 were Culex pipiens pallens, accounting for 89.72% of the total mosquito population, followed by 15 were Anopheles sinensis, accounting for 0.32%; 10 Aedes albopictus, accounting for 0.21%; 460 other mosquito species, accounting for 9.75%. Mosquito density was higher in rural areas compared to urban areas, with the highest density found in livestock sheds, followed by parks, hospitals, farms, and residential areas. Adult mosquito was first observed in May, with the peak activity occurring from June to August. The double-layer net method captures only Aedes albopictus, with an average net trapping index of 2.99 mosquitoes/(net·h), and their activity was concentrated from June to September. The average Brayton Index (BI) from May to October was 15.95, with a peak occurring in July and gradually decreasing after August. Insecticide resistance monitoring found that Culex pipiens pallens in Liaocheng City exhibited low resistance to permethrin, deltamethrin, dithion, and beta cypermethrin, with beta cypermethrin having the highest resistance. Conclusion　The dominant mosquito species in Liaocheng City is Culex pipiens pallens, followed by Aedes albopictus. The peak activity of adult and juvenile mosquitoes is concentrated between July and September, showing a distinct seasonal trend of growth and decline, posing a risk of dengue fever outbreaks. Culex pipiens pallens exhibits resistance to some insecticides, and timely measures should be taken to prevent the outbreak of mosquito-borne infectious diseases.