The feasibility and performance of food waste and sewage sludge co-digestion were investigated to gain insight into their resource utilization. In this study, two-phase anaerobic digestion (TPAD) was operated under a total solids mixing ratio of 1:1 and different sludge retention times (SRTs). Results show that an acidogenic reactor with a 5-day SRT obtained the highest acidification efficiency, and its acetic acid content was dominant. The organic removal rate of a methanogenic reactor (MR) with a 20-day SRT and its corresponding TPAD system with a 25-day SRT were both the highest among the MRs and TPAD systems. Volatile solids and total chemical oxygen demand average removal efficiencies of the TPAD system with a 25-day SRT reached 64.7 and 60.8%, respectively. The MR with a 30-day SRT obtained the minimum ratio of volatile fatty acid to alkalinity (0.12). The methane content generated from the different MRs fluctuated at around 70%. All of the above results can provide reference for future research.