The valence band shift in Pb1-xSrxTe thin films with different Sr compositions was studied. The ratio of conduction band offset and valence band offset in this heterostructure has been determined. Without considering the strain effect, the conduction band offset ratio is Qc=ΔEc/ΔEg=0.71, and with considering the strain effect, the energy band of PbTe is degenerated into longitudinal and oblique valleys. The conduction band offset ratio for longitudinal valley is QLC=0.47 and for oblique valley is QOC=0.72, respectively. Pb1-xSrxTe/PbTe heterostructure has a type Ⅰ alignment at the interface, which implies the confinement of both electrons and holes. The accurate determination of band alignment of Pb1-xSrxTe/PbTe heterostructure has great benefits in the research and development of mid-infrared opto-electronic devices.