The (Al0.1Ga0.9)0.5In0.5P, four-element alloy, whose band is direct, is used to make optoelectronic devices. The wavelength of the material is about 630nm. When it is epitaxially grown by low press-metalorganic chemical vapor deposition(LP-MOCVD), its quality will depend on temperature, one of the most important conditions. So it is essential to find out the best temperature of growth. The quantum wells of the (Al0.1Ga0.9)0.5In0.5P are grown at 700 ℃, 680 ℃, 670 ℃ and 660 ℃ respectively. The best temperature, which is found out by the results of photoluminescence PL, is about 670 ℃. The reasons are given by the results of PL, surfaces of wafers and the flow field simulation of MOCVD. The revaporization of In at high temperature and the incorporation of O at low temperature can lead to bad quality. An available path to solve growth at high temperature is to increase the effective density of In.