Based on the absorption mechanism of the semiconductor, the laser energy transition process in the semiconductor has been studied and a double-temperature model has been adopted to calculate the heating process in silicon irradiated by picosecond and nanosecond laser pulses respectively with the same energy density. A conclusion can been drawn from the calculated results that the carrier effect can be neglected and the heating process can be simulated through a single thermal conduction in the case of nanosecond pulse laser irradiation while the carrier effect must be take into consideration and a double-temperature model can be adopted in the case of picosecond pulsed laser irradiation.