The study examined the relationship between complement C3 level and abdominal aortic calcification in 456 patients with chronic kidney disease not on dialysis between 2019 and 2022. The results showed that patients with the third highest tertile of C3 (0.95–1.63 g/L) had a significantly higher risk of vascular calcification (OR = 2.06). The relationship between C3 level and aortic calcification was J-shaped, indicating a complex and non-linear association. Older age, high blood pressure and high cholesterol were confirmed as independent risk factors. The C3 level had a sensitivity of 79.4% and a specificity of 76.7% in predicting vascular calcification. The study suggests that complement activation is associated with an increased risk of cardiovascular complications even in patients with chronic kidney disease without dialysis.