To study the HIV infection rate and relevant behavioural characteristics among drug users (DUs) in the 15 cities of China-Gates HIV/AIDS Program. By literature review from the public security sector and expert consultations, the size of drug using population was estimated, questionnaire was used to survey relevant behavioural characteristics of DUs, and blood specimens were collected for HIV, syphilis and HCV testing. In 2007, the number of registered DUs in the 15 cities was 176 004, while the estimated number was 477 989. DUs mainly used heroin and crystal meth. Of the survey subjects, 41.0% (2685/6155) had correct knowledge about HIV/AIDS, and Hangzhou 97.6% (410/420), Qingdao 85.5% (342/400), Wuhan 69.7% (308/442), Kunming 63.8% (255/400), Shanghai 45.4% (237/522), Xi'an 44.5% (178/400), Nanjing 38.8% (155/400), Beijing 36.5% (237/650), Guangzhou 29.5% (122/413), Haerbin 25.4% (114/447), Haikou 23.8% (96/402), Chongqing 22.4% (90/401), Sanya 20.0% (80/400), Tianjin 16.2% (41/253), Shenyang 9.8% (20/205), and the difference among the cities has statistical significance (χ(2) = 1482.833, P < 0.05). The rate of needle sharing at the last injection was 10.8% (665/6155), and Hangzhou 10.8% (45/420), Chongqing 26.4% (106/401), Guangzhou 2.6% (11/413), Shenyang 31.3% (64/205), Shanghai 0.4% (2/522), Kunming 10.8% (43/400), Beijing 10.6% (69/650), Tianjin 5.4% (14/253), Xi'an 3.3% (13/400), Wuhan 17.9% (79/442), Sanya 20.0% (80/400), Haikou 2.2% (9/402), Haerbin 8.5% (38/447), Nanjing 21.4% (86/400), Qingdao 1.5% (6/400), and the difference among the cities has statistical significance (χ(2) = 483.044, P < 0.05). Only 5.0% (8737/176 004) of DUs and 1.2% of HIV positive DUs participated in needle exchange. The HIV, syphilis and HCV infection rates were respectively 2.76% (155/5620), 3.38% (190/5620) and 32.35% (1818/5620). The HIV infection rates of different city was:Hangzhou 0.4% (1/273), Chongqing 7.5% (30/401), Guangzhou 2.9% (12/413), Shenyang 0.5% (1/205), Shanghai 0.32% (1/316), Kunming 16.25% (65/400), Beijing 2.6% (16/624), Tianjin 2.0% (5/253), Xi'an 1.25% (5/400), Wuhan 0.24% (1/411), Sanya 1.75% (7/400), Haikou 0.2% (1/402), Haerbin 1.1% (5/447), Nanjing 1.1% (3/275), Qingdao 0.5% (2/400), and the difference among the cities has statistical significance (χ(2) = 354.203, P < 0.05). The HIV prevalence rate of IDUs in 15 cities slowly decreased although the HIV prevalence rate of IDUs in Chongqing and Kunming and other cities had surpassed the international warning level. The risk of sharing needles for HIV infection was dropped, and more attention should be paid to the potential risk of HIV transmission via unsafe sex due to the use of new drugs, such as amphetamine chloride.