Allergic purpura is a systemic vasculitis syndrome with small vasculitis as the main lesion. The main clinical manifestations are skin purpura, gastrointestinal mucosal bleeding, joint swelling and pain, and kidney damage (hematuria, proteinuria, etc.). The disease can occur throughout the year, but is more frequent in winter and spring. The disease can occur in all ages, and is most common in school-age children, with 3 to 14 years old being the most common age. It is more common in boys than in girls, with a male to female incidence ratio of approximately (1.4-2). Clinical characteristics 1, before the onset of the disease can have a history of upper respiratory tract infection or taking certain foods, drugs and so on. 2, the onset is more rapid, purpura is mostly seen in the distal lower limbs and buttocks, symmetrical distribution, different shapes, higher than the skin surface, pressure does not fade. It may be accompanied by urticaria, angioneurotic edema, wandering large joint pain, abdominal pain, blood in stool and hematuria, proteinuria, etc. 3.The majority of platelet count is normal or elevated, and bleeding, clotting time and clot contraction time are normal. 4, attention should be paid to regular urine examination, there may be microscopic hematuria, proteinuria and other manifestations of kidney injury. Renal tissue biopsy can determine the nature of renal lesions.