Abstract: Objective This study was conducted to investigate the scale of drug user population and learn the HIV infection of drug users Dali prefecture so as to provide science basis for comprehensive intervention for high risk behavior. Methods The scale of drug user population was investigated in the 12 counties(cities) using the nomination and multiple method, and the number of HIV infection among drug users was estimated with the Soft of Workbook 2007. Result There are 11 092 drug users totally in Dali Prefecture, in which 8049 injection drug users accounting for 72.57% of all. Now there are 5587 HIV infections among the drug users. Conclusion This research indicates that nomination and multiple method are all applicable and better tool, which are simple, convenient, reliable, cost-effective and labor saving in estimating the scale of high risk population related to HIV/AIDS infection. In order to decrease the bias of estimated result, we should pay attention to the influence of some factors on the result such as investigating time, representativeness of designated agencies, identification of target population and the standardization of investigation methods.