The rigid cell wall and low carbohydrate content of Taihu algae inhibit its application for hydrogen generation by anaerobic digestion (AD). In this study, algae was codigested with food waste (FW) in order to evaluate the influence of dried/wet condition and different mixing ratios on the digestion performance, where the dried algae (DA) showed an advantage over the wet algae (WA) by codigestion with FW. This was attributed to a suitable C/N ratio, more readily biodegraded organic substances, and microbial synergistic effect. The peak cumulative hydrogen production was 31.42 mL of H-2/g volatile solid (VS) when the FW/DA ratio was 40:10, which was 12.13 times higher than that from DA only (2.59 mL/g VS). Meanwhile, the codigestion group of FW/DA (40:10) showed the best performance, contributing to the highest value of 82.06% for the carbohydrate degradation rate, 95.54% for the protein degradation rate, and 11.60 g/kg for the total soluble metabolite concentration. During the DA codigestion process, it was found that the readily biodegradable materials in dissolved organic matter were utilized more fully and with the least amount of non-biodegradable matter content according to the excitation - emission matrix fluorescence spectra, which could provide a new insight into the bioutilization process of cosubstrates. Furthermore, codigestion selectively enriched hydrogen production bacteria and achieved high relative abundances of Clostridium sp. (78.46%) and Bacillus sp. (8.64%) for more efficient AD performance.