The invention relates to application of polyglutamine DNAJC7 to preparation of renal carcinoma diagnostic reagents or diagnostic equipment and belongs to the field of bioinstrumentation technology and medical diagnosis technology. According to the application, the polyglutamine DNAJC7 in serum is used as a molecular marker for diagnosing renal cell carcinoma, and a renal cell carcinoma patient can be accurately distinguished from healthy people, a chronic nephritis patient and a kidney stone patient. Therefore, the application provides an objective and accurate evaluation criterion for quick and accurate diagnosis of renal cell carcinoma and has the advantages of being simple in operation, low in cost, high in efficiency and free of side effects.