In the brazing-sintering process of the exploration diamond bit, the dimensions of the core mould, outer mould and the steel body directly determine that of the diamond bit and have a great influence on the use performance of diamond bit, while the study on the mould dimension design is not comprehensive in the existing literature. By the detailed research on heating and cooling process in the bit brazing-sintering, a set of more intuitive calculation formulae of mould dimension design and the methods to prevent mould from expanding crack are built up.