Objective Investigating the correlation between fluctuations in proliferation-inducing ligand （APRIL）， M-type phospholipase A2 receptor antibody （PLA2R Ab）， and 25-hydroxyvitamin D₃ ［25-（OH）D₃］ levels and their impact on the severity and prognosis of primary membranous nephropathy （PMN）. Methods A prospective study design was employed， wherein 100 confirmed PMN patients from Xingtai People's Hospital were recruited as the PMN group， and 100 healthy volunteers served as the control group. The levels of APRIL， PLA2R Ab， and 25-（OH）D₃ were compared between the two groups of participants， stratified by PMN disease stage and treatment outcomes. A simple linear correlation analysis was conducted to evaluate the correlation between APRIL， PLA2R Ab， and 25-（OH）D₃ with renal function indicators. Additionally， a multiple regression model was utilized to analyze the associations between these indicators and patient treatment outcomes as well as prognosis. Results The levels of APRIL and PLA2R Ab in the MN group were significantly higher than those in the control group， whereas the levels of 25-（OH）D₃ were significantly lower than those in the control group （P < 0.05）. Among 100 patients with PMN， there were 20 in stage I， 42 in stage Ⅱ， 34 in stage Ⅲ， and 4 in stage Ⅳ. The levels of APRIL and PLA2R Ab in stage Ⅲ+Ⅳ patients were significantly higher than those in stage Ⅰ+Ⅱ patients， while the level of 25-（OH）D₃ was significantly lower in stage Ⅲ+Ⅳ patients compared to stage Ⅰ+Ⅱ patients （P < 0.05）. In PMN patients， serum APRIL and PLA2R-Ab levels were negatively correlated with urea nitrogen （BUN）， creatinine （Scr）， and 24-h urinary protein （P < 0.05）. Additionally， APRIL and PLA2R-Ab levels were positively correlated with total protein （TP） and albumin （ALB） （P < 0.05）， while serum 25-（OH）D₃ levels were negatively correlated with BUN， Scr， and 24-h urinary protein （P < 0.05）. After treatment， 42 patients achieved complete remission， while 58 patients did not meet the remission criteria. Serum APRIL and PLA2R-Ab levels in the remission group were significantly lower than those in the non-remission group both before treatment and after 12 months of treatment. Furthermore， serum 25-（OH）D₃ levels in the remission group were significantly higher than those in the non-remission group both before treatment and after 12 months of treatment （P < 0.05）. Conclusions Elevated levels of serum APRIL and PLA2R antibodies， which contribute to immune dysfunction， are closely associated with the onset and severity of PMN. Renal impairment leads to a substantial reduction in serum 25-（OH）D₃ levels. Collectively， these three indicators serve as critical markers for the occurrence， progression， and prognosis of PMN.