In this work, lactose-based adhesive with excellent boiling water resistance was prepared by the Maillard reaction, free radical polymerisation and multiple cross-linking network strategy using lactose and biomass polyamino compound (MP) as raw materials. On the other hand, the branched P-N synergistic flame retardant coating was constructed using the developed MP reacted with aminotrimethylene phosphonic acid (ATMP), which was used to coat the surface layer of laminated composite to give it flame-retardant properties. The dry shear strength, 3 h hot water (63 °C) wet shear strength, and 3 h boiling water wet shear strength of the laminated composite were 2.23 MPa, 1.14 MPa, and 1.02 Mpa, respectively, which were in line with the requirements of GB/T 9846-2015 standard (≥0.7 MPa). In summary, this work provides potential methods for the preparation of environmentally friendly boiling water resistant lactose-based adhesive and branched P-N synergistic flame retardant coating which were used for the construction of high performance wood laminated composites.