To investigate the correlation between C3 deposition in mesangial area and renal pathology and immune indexes in children with Henoch-Schonlein purpura nephritis (HSPN), 249 children with HSPN who underwent renal biopsy in the pediatric kidney ward of the First Affiliated Hospital of Henan University of Traditional Chinese Medicine from January 2015 to December 2017 were selected. The levels of IgA, IgM, IgG, C3 and C4 in the serum were measured by immunoturbidimetric assay; the levels of CD3⁺, CD4⁺, CD8⁺ T cells were measured by FCM; the deposition of IgA, IgM, IgG, C3 and fibrin(Fib) in renal tissue were evaluated by immunofluorescence. The results showed that, according to the degree of C3 deposition, the patients were assigned to group A (－~±, 135 cases, 54.2%), group B (+, 83 cases, 33.3%) and group C (++, 31 cases, 12.4%). Among the 249 children, the distribution of renal pathological grade was as the following, 1 case in grade Ⅰ (0.4%), 41 cases in grade Ⅱa (16.5%), 18 cases in grade Ⅱb (7.2%), 100 cases in grade Ⅲa (40.2%), 79 cases in grade Ⅲb ( 31.70%), 9 cases in grade Ⅳ (3.6%) and 1 case in grade Ⅴ (0.4%). The degree of C3 deposition was positively correlated with renal pathological grade (r=0.127, P=0.045). In terms of immune indicators, serum complement C3 level was negatively correlated with the degree of C3 deposition in the mesangial region (r=－0.210, P=0.001). The differences in levels of IgA, IgM, C4 and IgG among various groups were not statistically significant (P>0.05). There were significant differences in levels of CD4⁺/CD8⁺T and C3 deposition between groups A and B, and also between groups A and C (P<0.05). CD4⁺/CD8⁺ levels were decreased in most children. There was no significant difference in serum CD3⁺, CD4⁺, CD8⁺T cell levels among different groups (P>0.05). Based on the above analysis, we conclude that the degree of kidney damage in children with purpuric nephritis is related to the deposition of C3 in the glomerular mesangial region. The stronger the C3 deposition, the heavier the kidney damage, and the lower the complement C3 level in the blood, reflecting the immunocompromised state of the patients.