The denitrification of bio-oil remains an important challenge in bio-oil quality upgrading. Microalgae (MA) and sweet potato waste (SPW) were co-liquefied to investigate the denitrification of Mannich reaction. The influence of interaction reaction between MA and SPW on products qualifies was explored. The results showed that the N contents of bio-oils from co-liquefaction (4.44-7.19%) were lower than that from microalgae (7.60%). Besides, the ester contents from MA&SPW (60.31-73.17%) were higher than that from MA (56.11%) and SPW (17.55%).The addition of SPW decreased the lubricating oil and fuel oil content. The experimental energy recovery efficiency (66.82-70.16%) was higher than the calculated energy recovery efficiency (65.68-66.69%) during co-liquefaction processes. Based on chemical compositions of products, a possible reaction pathway of Mannich reaction during co-liquefaction process was proposed. The current study suggested that co-liquefaction of microalgae and sweet potato waste was a feasibility way to improve the bio-oil quality and energy recovery efficiency.