Wettability controls the capillary behavior of injected CO2 including capillary entry pressure, relative permeability, and residual fluid saturation, and it is one of the most active topics in geologic carbon sequestration (GCS). However, the large uncertainty of water contact angle (CA) data and its pressure, temperature, and salinity dependence in the literature, limit our understanding on wettability. Molecular dynamics (MD) simulations have been performed to investigate the pressure (P) and temperature (T) dependence of water CAs on the silica surface. Three typical molecular surface models for silica, namely, Q(2), crystalline Q(3), and amorphous Q(3), were selected, and simulations were conducted at wide pressure (2.8-32.6 MPa) and temperature (318-383 K) conditions. The results show that P and T dependence of water CAs on silica surfaces is controlled by surface functional groups. These findings provide new information to help with the better understanding of wettability alteration under different GCS conditions.