he water-soluble amphiphilic random copolymer of P(DMA- co -VBC) with coumarin pendants has been designed to investigate the photo-induced dynamic association of coumarin pendants within polymer micelles in aqueous solution. Methods of absorption and emission spectra, solution transmittance, dynamic light scattering (DLS), and atomic force microscope (AFM) were applied. It was found that P(DMA- co -VBC) can form polymer micelles in aqueous solution. The time-dependent photo-dimerization degree (PD) of polymer micelles upon different intensity irradiations of 32002nm light showed saturating behaviors with an intensity-independent value of the maximum photo-dimerization extent, while the maximum photo-cleavage extent of coumarin dimers declined with the increasing intensity of 25402nm irradiation at used conditions. Furthermore, a significant emission band at 44502nm ( I 2 ) evidently emerged as against the disappearance of emission band at 38502nm ( I 1 ) during the photo-dimerization, and the time-dependent I 2 /I 1 ratios of polymer aqueous solution upon alternative irradiations of 320 and 25402nm light showed a wave-like increase as a function of irradiation cycles, indicating a wavy closeness of coumarin pendants within polymer micelles during the reversible photo-dimerization cycles.