Polyethylenimine-functionalized graphene oxide (PGO) was prepared via facile chemical cross-linking, and the physicochemical properties of PGO were investigated by multiple characterizations. PGO has a stable porous network structure, rich in amino-targeted functional groups, and can effortlessly adsorb anionic dyes. The sunset yellow dye was selected for batch adsorption experiment. The equilibrium adsorption amount of PGO for sunset yellow is as high as 791.38 mg/g, with the corresponding removal rate of 99%. After 5 adsorption-desorption cycles, the sunset yellow removal rate still maintains at 99%, indicating the excellent renewability of PGO. Adsorption interaction mechanism was visualized by quantitative analysis of the electrostatic potential on the surface, the molecule combined with frontier molecular orbitals, and the independent gradient model through quantum chemical theory calculation. It is shown that the intermolecular electrostatic interactions, hydrogen bonding and the van der Waals force of PGO and sunset yellow dye are efficient adsorption forces.