For enhancing the physical properties of water-based acrylic resin coating, a green modified water-based nano-alumina dispersion was successfully prepared by regulating mass fraction of anti-sedimentation dispersant under the condition of ultrasonication. Subsequently, the water-based nano alumina dispersion was characterized, and the physical properties of commercial water-based acrylic resin composite coating mixed with the dispersion were tested. Results showed that under the conditions of a dispersant mass fraction of 0.50% and an ultrasonic dispersion time of 0.5 h, the storage stability time of the prepared water-based nano-alumina dispersion was greater than 90 d. Besides, after adding 4%(mass fraction) water-based nano-alumina dispersion to commercially available water-based acrylic resin coatings, the wear-resistant rotation number of the as-obtained coating increased from less than 5 r to more than 15 r, and the scratch resistance load increased from 1.10 kg to 2.00 kg.