The invention relates to novel pharmacological action of sarsasapogenin in Rhizoma Anemarrhenae, i.e., prevention and treatment effect of sarsasapogenin on early-stage diabetic nephropathy. Sarsasapogenin can obviously improve damage to renal functions and morphology caused by diabetes; i.e., sarsasapogenin can substantially reduce excretion of urine protein, the index of kidney weight, the content of uric acid in serum, the levels of advanced glycation end products (AGEs) and interleukins 18 (IL-18) in renal cortices, thickening of the basilar membrane of the kidney (glycogen deposition), accumulation of extracellular matrixes (collagen type IV and fibronectin) and the levels of renal inflammasomes NLRP3 and activated caspase 1. Sarsasapogenin can be used for prevention and treatment of diabetic microangiopathy like early-stage diabetic nephropathy.