Concentration detections of Octyl p-methoxy cinnamate of the eleven cosmetics products have been investigated. From the UV-vis and fluorescence spectra, the chemical sunscreen reagents absorb the UV-B energy and release the UV-A energy. The quantum yield calculation of these cosmetics have been studied. In the selection of the sunscreen reagents to avoid second damage, the physical sunscreen reagents are better than the chemical sunscreen reagents.