To study the thermalization dynamics process of ferromagnetic thin films excited by femtosecond laser,numerical computation based on three-temperature (3T) equations with finite difference method was carried out,and the analysis of this process combining with the results of the femtosecond laser pump-probe experiment was given. A coefficient was introduced to characterize temperature dependence of the specific heat of spin system,and the rationality was analyzed in details. First,analytical research of reflectivity change of NiFe films was carried out and the modified model matched ultimately the experiment results of NiFe films. The laser power dependence of peak value of reflectivity change was studied. Also,the ultrafast thermalization dynamics of nickel (Ni) films with different thicknesses were investigated associated with the experimental results. When the thickness of thin film is less than the depth of penetration,electron,spin system and the balance value of the 3T system grow up obviously,and when the thin film is thicker,the thickness of ferromagnetic thin film hardly affects the thermalization dynamics.