Abstract: Pediatric constitution is closely related to the occurrence, development, treatment and prognosis of allergic purpura. The characteristics of physique not only have individual differences, but also have group convergence; the common physique of pediatric is characterized by delicate internal organs and unfilled form and qi; vigorous vitality and rapid development. The two most common clinical types of individual physique in children are lung qi deficiency and spleen qi deficiency. Only children with relatively weak constitution can take advantage of the deficiency to enter the body because of the weakness of the external guard and the inability to resist evil. This leads to the imbalance of yin and yang in the body, the disorder of the internal organs and the overflow of blood outside the veins, which leads to the occurrence of purpura. The most common type of allergic purpura is the wind-heat injury type in the early stage; if it develops further, it will be the blood-heat delusional type; if it recurs over time, it will develop into the qi non-regulation of blood type or yin deficiency fire type. The allergic purpura in children can often heal on its own, but a few are prone to recurrence, which is obviously related to the physical constitution of children who often have insufficient spleen and insufficient lung.