Fabricating ordered molecular films and further tuning their assembly behavior is important for constructing organic devices with diverse performances. By using high-resolution scanning tunneling microscopy, in this work, we demonstrate that well-organized vanadyl phthalocyanine (VOPc) films can be formed via ‘bottom-up’ molecular self-assembly on a binary alloy Ag₂Sb/Ag(111). The Ag₂Sb monolayer is prepared by evaporating Sb atoms on clean Ag(111) and followed by annealing. The VOPc molecules are deposited on the Ag₂Sb layer via thermal evaporation. The molecular configuration, structural and orbital characteristics of VOPc are clearly clarified at a submolecular level. It is found that initially the ordered VOPc membrane only exhibits the O-up adsorption configuration. Its square-shaped unit cell consists of five VOPc molecules where two adsorption orientations coexist with the horizontal axis of VOPc which is rotated by about 11° or 21° relative to the side of the unit cell. Due to the molecular dipole-dipole interaction, further-deposited molecules result in the assembly of the second-layer VOPc films with the O-down configuration and the square-shaped unit cell that contains only one VOPc molecule. Subsequently, due to the dipole-dipole interaction between layered molecules, following VOPc molecular layers adopt alternating O-up and O-down configurations as well as the square-shaped unit cell, similar to the case of the second layer. In addition, we find that the molecular orbitals overlap in each assembled molecular layer due to the π-π interaction which could facilitate the charge transport along the π stacking direction of VOPc. This research provides possibility to regulate the adsorption configuration and assembly behavior of functional organic molecules on metal surfaces by forming surface alloys.