Based on the wettability alteration caused by the modified hydrophobic solid surface, the phenomenon of wettability alteration is simulated numerically in terms of linear and instantaneous modification by using the lattice Boltzmann method which can properly reflect the interaction of solid-liquid molecules, combined with the volume of fluid method to dispose the quality of interface layer. Results show that the wettability changes smoothly in the process of linear modification, the time needed for wetting significantly decreases, and the relationship between the contact angle and attractive coefficient of solid-liquid accord well with literature data. The more greatly the amplitude of instantaneous modification changes, the stronger the force of solid acting on droplet is, which is reflected by the obvious change of wettability. It is also found that the contact angle changes exponentially with time after instantaneous modification, which is in good agreement with the existing conclusions. Further investigation shows that the liquid oscillation exists in the whole spreading process. The vibration peak is associated with the modified amplitude of linear modification. And liquid film velocity increases suddenly at sometime after instantaneous modification, which is associated with entrained air.