The invention discloses a segmented-assembling composite mold. The segmented-assembling composite mold comprises multiple segmented molds, locating pins and connecting pins. Each segmented mold is ofa frame type structure. The end of each segmented mold is provided with a butt joint plate. Each butt joint plate is uniformly provided with ventilating holes. After every two segmented molds are in butt joint, a welding step face is formed at the periphery of each ventilating hole in each butt joint plate. Locating holes and connecting holes are formed in the peripheries of the ventilating holes,and the multiple segmented molds are precisely located and fixedly combined together through the locating pins and the connecting pins. After the multiple segmented molds are in butt joint, welding is conducted on the welding step faces, the locating pins and the connecting pins, so that the mold is formed.