[Aim]  To clarify the occurrence, ecological habits, and distribution of muscid flies in pastures around Daqing and Qiqihar in Heilongjiang Province. [Methods]  We used sweep netting to collect flies from ten pastures. Both morphological and molecular techniques were used to identify species. Fly habitat preferences were assessed by placing traps in different pasture areas, and light traps were used to assess nocturnal fly activity. [Results]  A total of 3 875 flies were caught, and a total of four major fly species identified: Calliphora vicina, Helicophagella melanura, Musca domestica, and Neomyia cornicina. Monitoring from July to September 2024 revealed significant differences in fly numbers among pastures, with most found at the Xinhai Dairy Cattle Breeding Cooperative and the least at the Sanhe Livestock Breeding Co. Ltd. Factors such as manure management, feed residues, and environmental temperature and humidity, probably caused these differences in fly abundance. Ecological analysis showed M. domestica, C. vicina, and N. cornicina were active and phototactic during the day, whereas H. melanura was less light sensitive. H. melanura preferred fermenting plant residues, whereas C. vicina and N. cornicina favored high protein foods. M. domestica had broad food adaptability. [Conclusion]  In this study, four main flies in 10 dairy farms in Daqing and Qiqihar of Heilongjiang Province were identified, and their quantitative influencing factors and ecological habits were clarified, which provided scientific basis for precise prevention and control of flies in dairy farms.