The liquid lithium tin alloy is a promising breeder material for the tritium blanket of the fusion fission hybrid reactor (FFHR). For an effective design of the deuterium-tritium fuel circulation of FFHR, a mathematical model of kinetics of tritium desorption behavior from liquid Li25Sn75 alloy was built based on the action theory of metals and hydrogen. The calculation data of tritium desorption behavior under different operating conditions of temperature, tritium partial pressures, helium gas flow and mass transfer coefficients were obtained. The results show that the overall desorption process, even though including five sub-processes (transport of the tritium by diffusion and convection, transport of the tritium by diffusion through a layer of eutectic adjacent to the gas-eutectic interface, heterogeneous reaction at the interface of the tritium atoms recombination, diffusion of the tritium through the gas-phase boundary layer and transport of the gaseous tritium by diffusion and convection from the gas phase boundary layer), is governed by the diffusion of tritium atoms in the Li25Sn75 and by the heterogeneous reaction at the gas-eutectic interface of the tritium atoms recombination in the desorption temperature range from 673 to 873 K