The low temperature photovoltaic (PV) spectroscopy was used to study the optical transitions between subbands of strained In0.18Ga0.82As/GaAs quantum well,experimental results are well consistent with that of theoritical calculation. The dependence of PV peak transition energy on temperature has been analysed and the strain factor and conduction band offset Qc for quantum well have been found to be almost independent of temperature.The full width at half maxium (HWHM) of transition peaks as a function of temperature has been studied. From a good fit,we discuss the influences of the exciton phonon coupling,alloy disorder and interface roughness on the line shape.