Abstract: Abstract: Anaerobic co-digestion is an effective technology to solve the limitation of low biogas production from single substrate anaerobic digestion of agricultural biomass waste, owing to its inappropriate ratio of carbon to nitrogen. It is acknowledged that C/N ratio is one of the most important factors affecting the performance of anaerobic digester. Previous studies showed that the optimum range of C/N is 20-30 on anaerobic co-digestion. However, most of the literatures only investigated the effect of C/N ratio on biogas production and few studies focused on production performance of both biogas and slurry during anaerobic co-digestion process. Thus, this study explored the effect of C/N ratio on anaerobic co-digestion of pig manure and corn straw, taking both biogas production rate and nutrient content of slurry into consideration. A semi-continuous experiment was performed in a continuous stirred tank reactor (CSTR) with a working volume of 8 L under mesophilic temperature condition (37±1 ℃). Anaerobic co-digestion was operated at C/N ratio of 13.45 (pig manure as sole feedstock), 20, 25, 30, 35 and 300 (corn straw as sole feedstock). The results showed that anaerobic co-digestion system was seriously inhibited by the accumulation of volatile fatty when the C/N ratio of feedstock was 300 corn straw as sole feedstock. In addition, specific biogas production rates and total nutrient concentration of slurry were also very low, with the values of 46.00 mL/(g·d) and 518.92 mg/L, respectively. Whereas, CSTR system was stable and achieved a relative higher specific biogas production rates and slurry concentration at the C/N ratio of 13.45 (pig manure as sole feedstock), 20, 25, 30 and 35 than at the C/N ration of 300, in which the specific biogas production rates were 493.0, 438.81, 514.75, 485.32 and 467.88 mL/(g·d) and CH4 content were 67.30%, 63.99%, 63.31%, 59.96% and 57.40%, respectively. Compared with corn straw and pig manure as sole feedstock, specific biogas production rates were increased by 26.45%, 80.63%, 99.38% and 120.25% on anaerobic co-digestion systems with C/N ratio of 20, 25, 30 and 35, respectively. It was found that the anaerobic co-digestion of pig manure and straw could improve the performance of anaerobic biogas production, compared to the anaerobic digestion of a single material. Meanwhile, enough nutrients were contained in slurry. In summary, optimal co-production performance of biogas and slurry was obtained when the C/N ratio of feedstock is 25 on the anaerobic co-digestion system of pig manure and corn straw. The specific biogas production rate, methane content and total nutrient concentration were 514.75 mL/(g·d), 64.01% and 660.26 mg/L, respectively. This study provides technical parameters and practical guidance for the exploration of highly efficient technology for co-production of biogas and slurry from agricultural biomass waste.