Objective To investigate the prevalence and risk factors of reduced renal function among the population over 80 years old living in the communities of Chengdu City. Methods A total of 826 subjects were sampled from residents over 80 years old in the urban and rural communities of Chengdu City by stratified cluster sampling in the years of 2012 to 2013. Data were collected through questionnaires, physical examination, and laboratory tests for reduced renal function and relative risk factors. Results The prevalence of reduced renal function was 19.6% among the elderly over 80 years, and increased with age. Among those with reduced renal function, their awareness rate was 24.1% and the treatment rate was 11.1%. Multivariate logistic regression analysis indicated that diabetes, age, hypertension, overweight or obesity were identified as independent risk factors associated with reduced renal function among the elderly. Conclusion Reduced renal function is quite common among the elderly over 80 years in Chengdu communities. It is of importance to strengthen the monitoring of renal function in the elderly. The awareness rate and the treatment rate of reduced renal function are very low in the elderly. It is of important significance to prevent and treat diabetes and hypertension, and to control overweight and obesity in the elderly, so as to lower the incidence and development of reduced renal function.