The invention belongs to the technical field of wood modifier synthesis and provides a multifunctional wood modifier which comprises a compound I. The compound I is of a structure shown as follows. The invention further provides a preparation method of the wood modifier. The preparation method includes: using cyanuric chloride, n-hexylamine, taurine and 3-mercapto-1, 2, 4-triazole as raw materialsto synthesize the compound I through three-step reaction. The invention further provides application of the wood modifier in being impregnated in rubber wood. The multifunctional wood modifier has the advantages that a flame retardant has flame-retardant, smoke-inhibiting, bacteriostatic and moistureproof effects and is high in flame-retardant efficiency and low in cost; the modifier has high impregnation resistance when being added into the rubber wood and has no impact on using performance of the rubber wood; the modifier can form nitrogen-sulfur synergistic flame-retardant effect and is simple in synthesis process and suitable for popularization and application.