The invention discloses a deep water pipeline composite polyurethane elastomer heat insulation layer casting molding device. A subsection machining and integral assembly mode is adopted in a die, heating temperature control devices are arranged corresponding to subsection assemblies in subsections, and heating oil passages are arranged opposite; a positioning structure and a sealing structure arearranged in the parting surface of the die; and the die is provided with a die opening device, a die closing and an inclination device controlled by a hydraulic system. The device realizes mechanicaloperation of casting molding of a product, and has practical structure and strong operability; by adopting subsection machining in the die, the machining difficulty and the machining cost are reduced, and the machining precision and the machining quality are improved; and meanwhile, three sets of heating devices are used corresponding to three sections of assemblies, so that the heating temperature difference is reduced, the quality of the cast product is improved, automatic control of the temperature of the casting die can be realized, the heat insulation time of the polyurethane heat insulation layer in the die is shortened, and the service efficiency of the casting die is improved.