Objective To explore the changes of kidney function with aging in a large-scale physical examination population in a county of north part of Jiangsu Province. Methods A retrospective cross-sectional study was performed based on the data of 31 593 people taking physical examination at the Sheyang County People′s Hospital from February 2018 to December 2019. They were divided into 6 age groups:18-29,30-39,40-49,50-59,60-69, and 70+ years old groups. Eestimated glomerular filtration rate (eGFR) was obtained using the Chronic Kidney Disease Epidemiology Collaboration equation based on serum creatinine equation. The decline slope of eGFR with aging was assessed by linear regression analysis. Chi-square test was used to compare the annual average rate of decline between groups. The incidence of eGFR <90 ml/(min·1.73 m²) in different age groups was compared by linear trend Chi-square test. SPSS statistics 26.0 was used for statistical analysis. Results A total of 29 167 adult participants were included finally. eGFR was decreased with age at an average annual rate of(0.82±0.00) ml/(min·1.73 m²). The annual decline rates were(0.64±0.07),(0.69±0.04),(0.78±0.03),(0.78±0.03),(0.87±0.06) and(1.03±0.06) ml/(min·1.73 m²), respectively in the age groups. The rate of decline was increased significantly in the 70+ years old group (P<0.05). For the subjects with serum creatinine(SCr)and blood urea nitrogen(BUN) in the normal reference ranges, the incidence of eGFR <90 ml/(min·1.73 m²) were 14.73% and 12.27%, respectively. The prevalence of eGFR <90 ml/(min·1.73 m²) was increased with aging, and was 13.00% for overall subjects. The incidence was 0.27%, 0.86%, 5.43%, 13.28%, 32.30% and 86.45% for each age group, respectively, with statistical differences according to the results of linear trend Chi-square test (P<0.05). The incidence of eGFR <60 ml/(min·1.73 m²) in the 70+ years old group was 10.84%. Conclusion eGFR is significantly decreased with aging. The incidence of eGFR <90 ml/(min·1.73 m²) is higher in the elderly. An integrated application of SCr, BUN and eGFR is recommended for the assessment of kidney function.