The photoluminescence of InAs/GaAs submonolayer structure was measured at 15K under hydrostatic pressure up to 8 GPa. At normal pressure, the peak energies of the heavy hole exciton emission have a blue shift with the decrease of the thickness of the InAs layer, and with a narrowing peak width and weakening peak intensity. The pressure behavior of these peaks is similar to that of the GaAs matrix, indicating that the model of quantum well (quantum wire, quantum dot) structure is still valid for InAs/GaAs submonolayer. The increases of the confined energies for electrons and heavy holes are 23 and 42 meV, respectively, for 1/3 monolayer InAs/GaAs sample due to the additional lateral confinement of carriers.