Urinary protein excretion in normal people is <150mg/day, beyond this range is defined as proteinuria. Proteinuria is mainly divided into two categories, namely physiological proteinuria and pathological proteinuria, as follows: 1. Physiological proteinuria: it is common in strenuous exercise, fever, high temperature or cold environment, when there is no problem with the kidneys and no harm to the human body; 2. Pathological proteinuria: it is mostly caused by kidney diseases, such as problems with the barrier function of the kidneys, where protein in the blood is leaked into the original urine and discharged later; problems with the function of the kidney tubules. The abnormal ability to reabsorb protein can also lead to proteinuria. In addition to kidney problems, abnormal protein in the blood, which is filtered by the kidneys and exceeds the reabsorption capacity of the renal tubules, can also manifest proteinuria, and this condition can also lead to kidney damage at a later stage. In conclusion, there are two main reasons for the occurrence of proteinuria, one is the increased filtration by the kidneys and the other is the decreased reabsorption capacity of the renal tubules. Generally, after the appearance of pathological proteinuria, a renal puncture biopsy is needed to clarify the diagnosis and further treatment.