Abstract: In order to decrease the bremsstrahlung radiation intensity, the bremsstrahlung intensity of strontium-90 isotope radiation source is calculated by MCNP, and the dose equivalent rate of the surface bremsstrahlung is obtained. According to the properties of bremsstrahlung, the intensity of bremsstrahlung is positively correlated with the atomic number of the substance when beta particles interact with the substance to produce bremsstrahlung. So we consider adding some materials with low atomic number into the isotope radiation source, such as graphite, to reduce the bremsstrahlung radiation produced by the isotope radiation source, and use MCNP to calculate the dose equivalent rate of the source after incorporating with carbon. Calculated by MCNP, the equivalent rate of bremsstrahlung radiation dose of strontium-90 radiation source decreases to a certain extent when graphite is doped.The research and calculation results will provide some reference for the design of Sr-90 isotope radiation source.