A combined process consisting of an enzymatic pretreatment of small poplar wood chips, followed by an ultrasonic treatment was proposed and performed. Under the ultrasonic action of cavitation, thermal, and mechanical effects, the two processes of pulping and bleaching can be completed in one procedure. Before the ultrasonic treatment assisted pulping, an enzyme pretreatment was used to destroy the bonds between the cellulose, hemicellulose, and lignin to make the subsequent ultrasonic treatment exhibit higher selectivity and efficiency. This provided a poplar ultrasonic assisted pulp (PUP) with a 75% yield. A further analysis of the pulp, utilizing a scanning electron microscope (SEM), showed the fine fibrillation degree of the fiber surface of PUP was comparable to the traditional poplar chemimechanical pulp (PMP) and poplar chemical pulp (PCP). Thermogravimetric analysis and Raman analysis showed that the final residue obtained from the PUP was 20%. In addition, a decorative base paper was successfully made using the poplar ultrasonic pulp, and the physical properties reached or exceeded the industry standard of decorative base paper.