Femtosecond laser surface texturing of materials by means of direct laser ablation has received a wide range of applications, not only in surface wettability control but also for virus and bacterial repulsion. The wettability of laser-textured surfaces, however, experiences changes with time due to changes in surface chemistry such as oxidation and/or molecular adsorption, and these processes are not yet sufficiently studied. For example, it is widely known that after laser treatment, surface oxidation changes frequently lead hydrophilic surfaces to become hydrophobic surfaces on a time scale of a few days to many weeks. In this work, we proposed a detailed atomistic simulation method such as reactive molecular dynamics to simulate the physical-chemical changes, in particular, surface oxidation and molecular adsorption at the interface of Ti/TiO2 by femtosecond laser ablation. The simulation results show that oxygen transport is the dominant process during the initial oxidation, and after bond breaking, the oxygen atom is adsorbed to the surface of Ti to make the surface oxidized, thus changing the surface energy. The results obtained from this simulation provide explanations for several experimental results. These simulations are shown to be promising for explaining the wetting transition mechanism for laser-textured materials. [1] Samanta, A., Wang, Q., Shaw, S. K., & Ding, H. (2020). Materials & Design, 192, 108744. [2] Bizi-Bandoki, P., Valette, S., Audouard, E., & Benayoun, S. (2013). Applied Surface Science, 273, 399-407. [3] Huygh, S., Bogaerts, A., Van Duin, A. C., & Neyts, E. C. (2014). Computational materials science, 95, 579-591.