Abstract: Based on neutron transport code MCNP and ENDF/B-Ⅶ-1 database, Doppler coefficients of typical inert matrix fuel (IMF) were calculated and expressions of isotopic contributions to Doppler coefficient were given by theoretical analysis. The results indicate that absolute Doppler coefficient of weapon-grade plutonium IMF is smaller than that of reactor-grade plutonium fuel. The additive of ²³²Th makes the Doppler coefficient more negative which is similar to UO₂ in quantity. The contribution of boron burnable poison to Doppler coefficient is positive, however, erbium burnable poison can further enhance the negative Doppler coefficient, which is conducive to reactor inherent safety.