This paper investigated the co-digestion system stability of municipal biomass waste and the effects of inhibitory factors. It takes the mixed urban biomass of kitchen, fruits and vegetables waste and municipal sludge with the feed ratio of 1:1:1 as the research subject, and studies the influence of organic load and residence time on the stability and biogas production performance of the co-digestion system. Specific methanogenic activity is employed to test the microbial activity of anaerobic system and investigate the inhibition of VFA concentration and ammonia nitrogen concentration on microbial activity. Studies show that within the load range of 3.0-13.0 kg VS·(m3·d)-1, the concentration of VFA in the discharge material shows an upward trend with the increase of organic load. However, due to the high alkalinity of the reactor, the reactor operates stably in the whole operation process without acidification and other instability phenomena. With the increase of the load, the biogas organic product production rate gradually decreases, indicating that the biomass gas production capacity is inhibited with the increase of the load. The inhibitory factors of the anaerobic digestion process are studied through the activity experiment of producing methane from sludge in the reactor, and the semi-inhibition concentration of organic acid and ammonia nitrogen on the anaerobic digestion process of biomass waste is obtained, among which the value of IC50 for acetic acid to anaerobic digestion is 2150 mg/L, for propionic acid is 1850 mg/L and for ammonia nitrogen is 4500 mg/L. In the actual reactor operation, the control of organic acids is the primary task. The results of this study provide technical supports for the stable operation of urban biomass co-digestion process and the control of inhibitory factors.