It is extensively accepted that limited intake of diet protein to reduce kidney hyperfiltration and renal glomerulus internal pressure is effective in delaying the progress of nephropathy. But at present, debate exists in clinical research papers (such as MDRDS) to the role of low protein diet in delaying the progress of nephropathy. Adding compound α-Keto Acid tablet to low protein diet for patients can prevent essential amino acid deficiency and ameliorate severity of metabolism disorder, thus prevent malnutrition. Compared with standard diabetic diet, the aim of this study is to evaluate the efficacy and safety of compound α-Keto Acid tablet in combination with low protein diet in delaying the progress of nephropathy.