Wood-based panels have been widely used in our daily life, whose performances are mainly determined by wood adhesive. However, the commonly-used formaldehyde-based adhesives nearly confront the challenge of formaldehyde release. In this paper, a novel bio-based adhesive tannin-citric acid (TCA) adhesive was prepared from tannin (TA) and citric acid (CA). The preparation parameters, such as mass ratios of CA/TA, hot-pressing temperatures, and hot-pressing time, for synthesizing the TCA adhesives and preparing the plywood were optimized. When the mass ratio of CA/TA was 0.6/1, the hot-pressing temperature was 200 °C, and the hot-pressing time was 4 min, the plywood bonded by TCA adhesive showed favorable performances with dry strength, cold water (20 °C) strength, and hot water (63 °C) strength of 1.27 MPa, 1.25 MPa, and 1.40 MPa, respectively. These properties are satisfied with the Chinese National Standard (GB/T 17657–2013). For its sustainability and feasibility, the prepared TCA adhesive shows great potential for preparing high-performance wood-based panels in industry.