Photoluminescence (PL) measurements on CdTe/GaAs heterostructures grown by molecular beam epitaxy (MBE) were carried out to investigate the effect of the lattice mismatch and the thermal expansion on the strain due to the CdTe epitaxial layer thickness in CdTe/GaAs heterostructures. The PL peak of the acceptor bound exciton shifts toward the higher-energy side with increasing CdTe film thickness. A new theoretical equation obtained from the strain on the lattice-mismatched heterostructure is proposed. The values of the strains determined from the PL measurements were in reasonable agreement with those determined from the new theoretical calculations taking into account the lattice mismatch together with the thermal expansion difference between the CdTe epilayers and the GaAs substrates. These results can help improve the understanding of the structural properties of CdTe/GaAs heterostructures.