Electrically controlled solid propellant (ECSP) is a novel and potential propellant with excellent properties, which can achieve multiple ignitions and extinguishments through supplying and cutting electric power. At present, thermochemistry coupled with electrochemical reaction processes are complex and not understood clearly, especially its based thermal decomposition mechanism without electric power. In this work, the baseline ECSP was prepared using lithium perchlorate (LiClO4, LP) as oxidant, and tungsten as metal additive to obtain high energy ECSP samples. The scanning electron microscope (SEM), energy dispersive spectroscopy (EDS), differential scanning calorimeter (DSC) and thermogravimetry (TGA) were used to investigate thermal analysis characteristics of ECSP and the effect of tungsten sizes on reaction process and mechanism. The heat release and effective activation energy (Eα) of baseline ECSP were lower than those of metalized ECSP. In addition, with W size increasing, heat release and Eαincrease. Based on thermal analysis and kinetic results, the decomposition mechanisms of ECSP main components and samples were proposed. The absorbed and crystal water evaporated, then main components molten for all cases at low temperature (< 250 °C). With the temperature rising, baseline ECSP occurred to three-stage reaction (7 step reactions), while metalized ECSP shown rapid one-stage reaction (3 step reactions).