The design of polymers from renewable plant oils is gaining more attention within sustainable development. Most plant oils based thermoplastic polymers exhibit poor mechanical properties. In this paper, we reported the mechanically strong cellulose-graft-soybean oil copolymers, which combined two natural biomasses in one. The soybean oil-based monomers with secondary amide groups (SOM1) and tertiary amide groups (SOM2) were prepared and copolymerized. The mechanical properties of the P(SOMl-co-SOM2) copolymers were investigated. Cellulose-g-P(SOMl-co-SOM2) copolymers with 0.5 wt% cellulose were prepared via atom radical transfer polymerization. FT-IR, H-1 NMR, and TGA measurements demonstrated that the Cellulose-g-P(SOMl-co-SOM2) copolymers were successfully prepared. Tensile test results demonstrated that the mechanical properties of the as-prepared Cellulose-g-P(SOMl-co-SOM2) copolymers were superior to the linear P(SOMl-co-SOM2) copolymers.