Abstract: The flame retardance treatment and mechanical enhancement of wood composites have been widely concerned. The addition of flame retardants not only increases the viscosity of the adhesive, but also the reactive groups in the flame retardant can be chemically cross-linked to the resin molecules, hindering the polymerization process of the adhesive, which affects the curing process of the resin. Through the modification of the flame retardant, it can improve the curing reactivity and enhance the bonding strength of the adhesive, while minimize the migration of the flame retardants, effectively improve the flame retardant properties and mechanical strength of the materials. Herein, we prepared polyelectrolyte complex polyethyleneimine (PEI)/ammonium polyphosphate (APP) by self-assembly using APP and PEI as anionic and cationic polyelectrolytes, and further applied it to wood particle board. PEI/APP enhances the curing reactivity of urea formaldehyde resin (UF) and simultaneously endow particle board with excellent mechanical strength and flame retardant properties. The activation energy (E_a) of UF and different PEI/APP additions are calculated based on Kissinger and Ozawa kinetic equations, focusing on the effect of PEI/APP on UF curing kinetics. It is indicating that PEI/APP and UF formed a molecular crosslinking network through amide bonding and hydrogen bonding, facilitating the condensation and curing process of UF, resulting in E_a decreasing gradually with the increase of the content of PEI/APP, the curing reactivity increasing gradually and the curing exothermic peak temperature (T_P) of UF decreasing gradually. Meanwhile, the cross-linked network formed between PEI/APP and UF enhanced the cohesive strength and interfacial bonding of wood particles, and the physical and mechanical properties of particle board were improved significantly. When the content of PEI/APP is 10wt%, the particle board has the highest modulus of elasticity (MOE) and modulus of rupture (MOR), which are 3368.46 MPa and 27.18 MPa respectively. Meanwhile, the limiting oxygen index (LOI) of the particle board reached up to 46.3%, and the peak heat release rate (PHRR) was reduced to 170.3 kW/m², which were 45.3% and 22.3% lower than that of the untreated and APP treated particle board, respectively. The PEI/APP heat-generated polyphosphoric acid is capable of causing the organic matter to dehydrate and char, resulting in a swollen carbon layer, whose dense and continuous inner and outer layers effectively prevent heat and mass transfer between the gas and condensed phases. PEI/APP facilitates the curing of UF at lower temperatures and simultaneously endows particle board with excellent process, flame retardant and mechanical properties. Finally, the economic composition of flame retardant particle board was analyzed.