Optical band gap or band gap is an important characteristic parameter of semiconductor materials. In this study, several representative InGaN/GaN multiple quantum well structures are taken as the research objects, and the test conditions that need to be met for the luminescence measurement of the optical band gap of the InGaN well layer at a certain target temperature are discussed in depth. Since the InGaN well layer is a multi-element alloy and is subjected to stress from the GaN barrier layer, there exist not only impurity/defect-related non-radiation centers in the well layer, but also localized potential fluctuation induced by composition fluctuation and quantum confinement Stark effect (QCSE) induced by polarization field. Therefore, in order to obtain a more accurate optical band gap of the InGaN well layer, we propose the following test conditions that the luminescence measurement should meet at least, that is, the influence of the non-radiation centers, the localized centers and the QCSE on the emission process at the target temperature must be eliminated. Although these test conditions need to be further improved, it is expected that this test method can provide valuable guidance or ideas for measuring the semiconductor optical band gap.