The invention relates to the field of chemical engineering, and particularly discloses a polyurethane adhesive, a preparation method thereof and an aluminum cellular plate. The polyurethane adhesive comprises a component A and a component B, and the component A comprises the following raw materials: a hydroxyl-terminated polyurethane prepolymer, polyether polyol, a powder water absorbent and an inorganic filler. The polyurethane adhesive prepared by the preparation method disclosed by the invention has excellent bonding strength. By compounding a hydroxyl-terminated polyurethane prepolymer synthesized by adopting a prepolymerization method with bisphenol A/propylene oxide polyether glycol, the bonding strength and the flexibility of the polyurethane adhesive are ensured, mechanical strength is high, after curing for 60 days, the peeling strength and the plane tensile attenuation of the roller are not greater than 10%, the polyurethane adhesive can be widely applied to the field of aluminum honeycomb plates, the problem that the bonding strength of the cured polyurethane adhesive is attenuated when an existing polyurethane adhesive is assembled into an aluminum honeycomb plate is solved, and the provided preparation method is simple, low in cost and free of pollution to the environment.