Abstract: Phytic acid (PA) is a very promising phosphorus-based aqueous bio-based flame retardant, but its treatment of wood alone has problems such as easy loss of PA and high release of combustion smoke. This challenge can be mitigated to some extent by compounding with other nitrogen and boron flame retardants. However, due to the strong acidity of PA, PA and its complex flame retardants used in wood fire-retardant treatment may cause wood degradation, which in turn affects its mechanical strength. In this study, a new type of phosphorus-nitrogen flame retardant, amidinourea phytate (AUP), was synthesised from PA and dicyandiamide. The physicochemical properties of AUP was characterised using FTIR, XRD, XPS and TG. The effects of AUP on the pyrolysis and combustion behaviours of poplar wood were investigated by TG, Py-GC/MS, limiting oxygen index tester and CONE, and the flame retardant mechanism was explored. The results showed that the AUP flame retardant wood showed excellent flame retardant and smoke suppression properties at a lower weight gain rate (8.73%) than the PA flame retardant wood with a weight gain rate of 14.8%, and the loss resistance was better; the LOI value of the AUP flame retardant wood was 34.8%, which was 54.0% higher than that of the untreated wood; the total heat release and the total amount of smoke production were reduced by 57.7% and 65.7%, respectively, and the charcoal rate was increased by 148%, and the residual charcoal structure was more compact. The total heat release and total smoke production were reduced by 57.7% and 65.7% respectively, and the char formation rate was increased by 148%, and the residual char structure was denser, with the effect of cohesive phase and gas phase. In addition, the impact strength of AUP flame retardant wood increased by 58.5% compared with that of untreated wood, while that of PA flame retardant wood decreased by 29.2%.