Proteinuria (proteinuria) is a typical symptom of chronic kidney disease, and the cause of proteinuria is inextricably linked to the barrier function of the glomerulus. The glomerular capillaries are composed of three layers: the endothelial cell layer, the basement membrane layer, and the epithelial cell layer, from inside to outside. Since these three layers are distributed with filter pores of different sizes and negative charges, the barrier function of glomerular capillaries can be divided into two types, namely, mechanical barrier – filter pores and charge barrier – negative charges. Low-molecular proteinuria is caused by impairment of renal tubular function, resulting in impaired reabsorption of protein filtered through the normal glomerulus. Diagnosis: Low-molecular protein accounts for about 70% of the urine, while albumin accounts for only 15-25%. Urine protein quantification is usually at 1g/24h and rarely exceeds 2g/24h. Differentiation: The major difference with glomerular proteinuria is that low molecular protein in the urine accounts for about 70%, while albumin accounts for only 15-25%. Urine protein quantification is usually at 1g/24h and rarely exceeds 2g/24h. Low-molecular protein in the urine accounts for about 70%, while albumin accounts for only 15-25%. Urine protein quantification is usually at 1g/24h and rarely exceeds 2g/24h.