Background: The National Free Antiretroviral therapy (ART) Program in China has initiated to provide ART to HIV-1 patients, which may cause problems with drug resistance (DR). The number of HIV/AIDS patients in Chengdu ranks first in the national capital city. However, there is little data on the prevalence of HIV-1 DR in this region. Therefore, epidemiological surveillance was conducted on HIV-1 DR among patients receiving ART in Chengdu. Methods: From 2014 to 2016, HIV/AIDS patients (15 years and older) who had received first-line ART for at least six months were enrolled in this study. Demographic, behavioral information and medical history were recorded, and blood samples were collected for viral loads and immune cell count analyses. HIV-1 pol was amplified, sequenced, and analyzed for HIV-1 subtypes and drug resistance-associated mutations (DRMs). Results: A total of 13,782 individuals were enrolled and 653 cases were considered treatment failure after 6 months of ART. 481 (481/653) samples were amplified and sequenced successfully for subtypes and drug resistance analysis. Six subtypes were identified, among which CRF01_AE (54.3%) and CRF07_BC (41.6%) were the dominant subtypes, and CRF55_01B was detected in Chengdu for the first time. The overall prevalence of HIV-1 DR was 1.8%, with 1.2% to nucleoside reverse transcriptase inhibitors (NRTIs), 1.7% to non-NRTIs (NNRTIs) and 0.14% to protease inhibitors (PIs). The leading DRMs observed in the study were M184I/V (59.59%) against NRTIs and K103N (37.55%) against NNRTIs. Conclusions: This study focused on the HIV-1 molecular surveillance among treatment-experienced individuals in Chengdu. The overall prevalence of DR was relatively low among treated patients. These findings were believed to be contributed to an understanding of HIV-1 subtypes, DR prevalence and DRMs profiles in Chengdu, and thereby optimizing clinical management, prevention and control of HIV.