The ablation of silicon with femtosecond laser was numerically simulated. In the two-temperature model of the femtosecond laser interaction with silicon,band electron excitation,Auger recombination effect and two photon excitation etc. are introduced. The optical intensity at different time inside the material can be obtained with Maxwell equations in every optical half-cycle,and it is used as an input condition to the material equations that describe the response of the material for optical intensity. By using the iteration between Maxwell equations and the material equations,some parameters of the excited material are obtained,such as electron density and electron temperature. Under the ablation of picosecond and subpicosecond double-pulse and three-pulse femtosecond laser,the effect of laser energy density and pulse delay time on heat accumulation effect are analyzed.