The effects of carbon black, cupric adipate and RDX on the thermal decomposition behaviour of lead flake in double-base system are investigated by DSC measurement. The results show that the thermal decomposition peak of lead flake decomposition shifts to lower temperature with the addition of carbon black, cupric adipate and RDX, and the exotherm heat of lead flake increases with the addition of carbon black and RDX. DSC results are compared with the burning characteristics of practical plateau propellants, the chemical reactions involving lead salts near the burning surface are assumed. The mechanism of the effects of ballistic modifiers and RDX on the phenomenon of platonization are discussed.