The invention relates to a preparation method of a lasting air freshener and belongs to the technical field of fresheners. The preparation method mainly includes: drying and smashing plants like lysimachia foenum-graecum and semen cassiae; heating and stirring with hydrogen peroxide, adding cellulase, stirring and mixing, and discharging; mixing a discharged object with distilled water, and performing distilling, filtering and standing for layering to obtain supernatant; mixing and fermenting substances like roots of medical stone and cyperus rotundus, centrifuging for separation, collecting precipitate, treating the precipitate, and well stirring the precipitate with the supernatant and sodium alginate to obtain the lasting air freshener. The lasting air freshener prepared by the method is low in volatilization speed, daily volatilization amount is lower than 0.015g, and the lasting air freshener can be used for a long period of time; the lasting air freshener is nontoxic, environment-friendly and free of causing adverse irritation to human body.