Objective To explore the relationship between msangial C3 deposition and pathological classification of IgA nephropathy. Methods We reviewed renal biopsy–proven patients between January 1, 2016 and December 31, 2019 in the Xijing Hospital. Patients were divided into the two groups，negative group (- or ±) and positive group (≥1+)，according to the intensity of C3 deposition in mesangial area of glomurili. Results The remaining 975 patients were included in the study. The incidence of C3 negative patients was 21.8%. Compared to the C3 positive group, there were lower serum creatinine, higher eGFR and serum C3 in the C3 negative group. The proportion of C3 negative patients was the highest in grade I (50.5%) of Lee’s grading system for IgAN, then gradually decreased, was the lowest in grade Ⅳ-Ⅴ(9.8%), and was increased in grade V (20.5%), which presented an “arytenoid” curve. Compared to the C3 positive group, there were less patients with M1、E1、S1、T1-2and C1-2 in the C3 negative group. Conclusions The relationship between the incidence of C3 negative patients and Lee’s grading system for IgAN present an “arytenoid” curve. The pathological lesion is mild or chronic in C3 negative patients.