In order to further reveal the transient evolution characteristics of silicon ablated by femtosecond laser, the theoretical model was established, and the numerical simulation was carried out. The results show that the femtosecond laser can excite a large amount of electrons with its density exceeding the damage threshold in the pulse duration. At that time, the lattice remains in a “cold” state until it reaches the melting point temperature as long as 1 ns order of magnitude. The temperature of electrons dramatically increases to 10⁴ K level in the laser pulse irradiation moment. And then the energy is released slowly to lattice and the thermal equilibrium is reached until 10 ns order of magnitude. The electron has two rapid warming processes. The first one starts from the free-carrier absorption, and stops at the electron-lattice energy coupling; the second one starts from the single photon and two photon absorption, and ends at the end of the pulse. It is found that the higher the temperature and density of electron are, the bigger the pulse energy is and the shorter the pulse duration is.