This study aimed to investigate the prevalence of overweight and obesity and its relationship with cardiovascular risk diseases among different sex and age groups in an urban Chinese adult population. A retrospective analysis was performed on 384,061 Chinese adults aged 20 years and older in Nanjing. The age-standardized prevalence of overweight and obesity was 42.8% and 13.2% in men and 23.9% and 6.6% in women. A gradually increasing trend was observed in the prevalence of overweight and obesity from 2008 to 2016, especially in individuals aged 20~39 years. Overweight and obesity were significantly associated with increased risks of dyslipidemia, diabetes mellitus, hypertension, and hyperuricemia. Age weakened such relationship for both genders, which spiked in individuals aged 20~39 years. For men and women aged 20~39 years, the OR (95% CI) of obesity reached 4.23 (4.01-4.47) and 5.29 (4.63-6.04) for dyslipidemia, 3.70 (2.97-4.60) and 6.38 (3.86-10.55) for diabetes mellitus, 6.19 (5.76-6.64) and 9.36 (7.86-11.13) for hypertension, and 3.66 (3.45-3.88) and 6.65 (5.70-7.74) for hyperuricemia, respectively. The increasing trend in the epidemic of overweight and obesity is a risk factor for cardiovascular risk diseases in Chinese adults, especially in individuals aged 20~39 years.