Under the dual pressures of climate warming and anthropogenic activities, lake eutrophication and algal blooms have expanded in the world, releasing large amounts of algal dissolved organic matter (ADOM). Its transformation is highly concerned in the field of lake carbon cycling. To reveal the role of photochemical transformation on the microbial transformation of ADOM in lakes, we compared the ADOM transformation in microbial treatment and natural light-microbial treatment. The differences in the transformation of ADOM in these two treatments were compared in detail through ultraviolet-visible spectroscopy, three-dimensional fluorescence spectroscopy-parallel factor analysis, and Fourier transform-ion cyclotron resonance mass spectrometry. In addition, microbial community was explored by 16S rRNA sequencing. The results showed that the solar irradiation greatly inhibited the dissolved organic carbon removal rate by microbial treatment (0.28 d^-1 vs. 0.75 d^-1 ). Changes in the fluorescent components and molecular composition demonstrated that photochemical and microbial processes compete significantly for peptide-like components and peptide-like compounds. In addition, only part (about 50%) of the photochemically generated molecules could be utilized by subsequent microbial processes. The bacterial diversity in microbial treatment was significantly higher than that of the light-microbial treatment. The significant correlation between the abundance of some bacteria taxa and DOM components suggested that the alteration of ADOM composition by photochemical transformation had a key influence on the structure of the microbial community. Our study revealed the inhibitory mechanism of natural light on the microbial transformation of ADOM, which is important to understand the carbon cycling within eutrophic lakes.