The photoelectric characteristics of solar cells can be changed after heated, which ultimately influence the converting efficiency of solar cell. Electroluminescence spectra of GaInP/GaAs/Ge triple junction solar cell under constant voltage are investigated in order to understand the working properties of such cells under concentration and heating condition. It is found that the luminescence peaks of GaInP top cell and GaAs middle cell change and reverse after the solar cells are heated. By considering the current-voltage characteristic and external quantum efficiency, the origin of this phenomenon is found to attribute to the introduction of deep level defects in the crystal. GaAs middle cell is found to be more tolerant to heat-induced damage than GaInP top cell.