The invention belongs to the technical field of poly(cinnamic alcohol) injection medicament application, and in particular relates to application of a poly(cinnamic alcohol) injection used as a cyst treatment medicament. Conventional cyst treatment methods mainly comprise surgical excision, laparoscopic excision and others, with the disadvantages of long incision, multiple bleeding, severe wound, high cost and easy recurrence. In the application of the poly(cinnamic alcohol) injection used as the cyst treatment medicament provided by the invention, the medicament therapy is used to replace surgery therapy, 1% of the poly(cinnamic alcohol) injection is injected into the endothelial cells with the secretory function in the cyst wall, thus resulting in aseptic inflammation and the cyst is solidified, hardened, adhered, closed and gradually absorbed so as to disappear. According to the invention, the cyst patients can be treated without hospitalization, and the high cyst recurrence rate caused by incomplete surgical excision is avoided.