The study was conducted to investigate how the hot-spot formation was caused by crack friction in composite solid propellant under mechanic impact. It was concentrated on processes of crack surfaces slip, crack growth and friction heating of closed crack driven by sheer stress, heat conduction, decomposition of solid propellant and its interaction with the gas-phase product. In view of the fracture mechanics, heat conduction and dynamics of thermal decomposition of solid propellant, the meso-scale hot-spot model of crack friction was established. By making numerical calculation of the model, the process and condition for hot-spot formation were discussed, from which it is concluded that friction between crack surfaces slip and crack growth can lead to formation of hot-spot in composite solid propellant.