For improving the bonding strength and water resistance of plywood bonded with soy protein adhesive (SPA), an amino polymer (AP) was synthesized using polyamines, and the AP was used to modify SPA to prepare a modified soy protein adhesive (MSPA) in this paper. The plywood was prepared using MSPA, and the effects of preparation technology of amino polymer and hot-pressing technology of plywood on the bonding strength of plywood were investigated. The results showed that the optimization preparation technologies of AP were as follow: the molar ratio of polyamine/modifying agents was 0.25/1, the pH value was 5, the reaction temperature was 70 °C, and the reaction time was 1.5 h. The optimization preparation technologies of plywood were that the hot-pressing temperature was 150 °C and the hot-pressing time was 60 s/mm. The bonding strength of plywood made from MSPA on the optimization preparation technology was 1.03 MPa, which meets the requirement of plywood type II (³0.7MPa). The MSPA bonded plywood had a rather low formaldehyde emission, which is close to that of wood itself.