Abstract: Radiation heating rate is one of the important input data for the performance research, thermal hydraulic and mechanical analysis of in-core special materials such as gray rods, therefore evaluation of radiation heating rate of in-core special materials is important for the research of new in-core materials. In order to improve the calculation precision of neutron and photon radiation heating rates, we developed a source code for a 3D Monte Carlo(MC) code, produced cross sections of special materials, established CAP1400 model, simulated and calculated radiation heating rate of special materials in CAP1400 by using MC code. The MC code calculates the radiation heating rate of special materials in CAP1400 more accurately, and it can give radiation heating rate distribution, which supports domestic design of in-core special materials such as gray rods and related components.