The photoluminescence (PL) spectra of self-assembled In_0.55Al_0.45As/Al_0.5Ga_0.5As quantum dots (QD) grown on (311)A GaAs substrate were measured. The type-Ⅱ character of PL related to the X valley was verified by excitation power dependence of peak position and the PL spectra under different pressure, which was attributed to the type-Ⅱ transition from X valley in Al_0.5Ga_0.5As to heavy holes in In_{0. 55}Al_0.45As.The high energy Γ-related transition was also observed above 70K and aasigned as the transition between Γ valley and heavy holes in In _0.55Al_0.45As.The X-valley split was discussed to interpret the observed second X-related peak under pressure.