The utility model relates to a chemical agent injection pipe system of an underwater manifold, which is characterized in that: the chemical agent injection pipe system comprises a glycol injection pipeline, a methanol injection pipeline, a medicine injection pipeline and an emptying pipeline which are paved on the inner side of the manifold of a production pipeline layer by layer from bottom up, wherein all the glycol injection pipeline, the methanol injection pipeline, the medicine injection pipeline and the emptying pipeline respectively include a main pipe; the main pipes are vertically arranged in parallel; a plurality of pairs of branch pipes are arranged at intervals along the main pipes; and each of the branch pipes is equipped with a gate valve. The chemical agent injection pipe system of the underwater manifold is dedicate and compact in arrangement, makes full use of the inner space of the manifold, reduces construction difficulty and enhances reliability of the underwater production manifold; in addition, the chemical agent injection pipe system of the underwater manifold can meet basic functions of the chemical agent injection pipe system of the underwater production manifold and is in accord with related standards, therefore, the chemical agent injection pipe system of the underwater manifold can be widely applied to underwater production manifolds of deepwater gas fields.