Abstract： Objective:To investigate the association between high-density lipoprotein cholesterol (HDL-C) and the risk of diabetes mellitus (DM) in Chinese adults.Methods:This study was a secondary analysis of a multicenter, retrospective cohort study using data from the Chinese health screening program in the DATADRYAD database. Between 2010 and 2016, 211833 Chinese adults aged 20 years or older were screened for diabetes at baseline in 32 sites and 11 cities across the country. Baseline HDL-C level was the target independent variable and the risk of DM at follow-up was the dependent variable. Cox proportional hazards regression analysis assessed the independent association between HDL-C levels and the risk of developing DM. In this paper, the generalized Additive Model (GAM) and the smoothing curve fitting method were used to study the nonlinear relationships. In addition, subgroup analyses were conducted to assess the consistency of the correlations among different subgroup and to further validate the reliability of the results.Results:After adjusting for potential confounding factors such as age, sex and body mass index, HDL-C level was positively correlated with the development of diabetes ( HR=1.43, 95% CI: 1.08-1.90, P=0.012). The level of HDL-C showed a non-linear relationship with the risk of DM, and the inflection point was 1.81 mmol/L. The HR (95% CI) of the left and right sides of the inflection point were 0.94 (0.56-1.55) and 2.54 (1.93-3.30), respectively. When HDL-C>1.81 mmol/L, HDL-C was positively correlated with the occurrence of DM. Each 1.00 mmol/L increase in HDL-C increased the risk of diabetes mellitus by 1.54 times ( P<0.001); when HDL-C<1.81 mmol/L, the risk of diabetes decreased by 6% for every 1.00 mmol/L increase in HDL-C ( P=0.798). Subgroup analysis showed that, in the age, male, BMI 24.5-52.7 kg/m 2 subgroups, all the systolic blood pressure subgroups, diastolic blood pressure 69-77 and 78-164 mmHg (1 mmHg=0.133 kPa) subgroups, total cholesterol 0.02-4.26 and 5.00-17.84 mmol/L subgroups, all the triglyceride subgroups, low-density lipoprotein 0-2.42 and 2.99-12.60 mmol/L subgroups, alanine aminotransferase 23.4-1 508.4 U/L subgroups, aspartate transaminase 0-19.7 and 24.8-1 026.2 U/L subgroups, all the urea nitrogen subgroups, creatinine 61.5-76.9, 77.0-1 116.6 μmol/L subgroups, never smoking subgroup, subgroup with frequent alcohol consumption or family history of diabetes mellitus, the effect values of HDL-C and the risk of diabetes mellitus in Chinese adults showed good stability (all HR>1.00). Conclusions:High levels of HDL-C are associated with an increased risk of DM in Chinese adults. When HDL-C is greater than 1.81 mmol/L, HDL-C is positively correlated with DM.