【Abstract】 Objective To illustrate the composition, seasonal fluctuation and the diversity of flies  at different habitants in different months in Nanchang. Methods Cage trapping method was used for the monitoring of fly density, and the species diversity index and evenness index were employed. Results The dominant species of fly were Musca domestica, Chrysomya megacephala and Lucilia sericata in Nanchang. There were two peaks in one year, one in May to June, and the other in  September. The species diversity index and the evenness index were the highest in May, reaching 0.4036 and 0.4229 respectively. In 4 different habitants, both indexes were the maximum in farm market, which were 0.4768 and 0.5280, respectively. Conclusion The population characteristics of flies can be reflected with the species diversity index and the evenness index.