Background: People with simple renal cysts (SRCs) are more likely to develop renal injury and dysfunction, but the mechanisms remain controversial, as the process of SRC formation and its characteristics are not yet well-known. This research focuses on the characteristics of SRCs and discusses how SRCs cause renal injury. Methods: In 2014, a total of 401 participants without any prior kidney disease were selected for the research. Their average age was 49.7 years. SRC morphology and changes were monitored over a 5-year follow-up period. Renal volume and blood perfusion were measured by ultrasound imaging. Logistic regression analysis was used to assess the relationship between renal cyst and renal function. Results: During the 5-year follow-up, elderly participants with multiple cysts (odds ratio [OR] 1.89; 95% CI 1.67 to 5.99) and a maximum cyst diameter of 1.5 cm or greater (OR 1.93; 95% CI 1.15 to 5.34) were found to be positively correlated with renal injury. A decrease in intrarenal perfusion was observed at the early stages of follow-up, but the reduction in renal volume was a slow and gradual process. Conclusion: Elderly people with multiple cysts, a maximum cyst diameter of the cysts≥1.5 cm, and multiple cysts are more likely to suffer renal injury. Ultrasound examination has an important status in monitoring the changes in renal volume and peak systolic velocity (PSV) of the renal interlobar artery.