The invention discloses biodegradable multifunctional oil-absorbing particles capable of floating on a water surface and a preparation method thereof. The preparation method comprises the steps of preparing a mixed solution F from a NH4HCO3 solution, a NH4H2PO4 solution, a Ca(NO3)2 solution, a NH4OH solution, a hydrochloric acid solution, a NH4Cl water solution and an ethylenediaminetetraacetic acid calcium potassium solution; preparing a mixed solution L from urea and a formaldehyde water solution; preparing a mixed solution M from a poly beta-hydroxybutyrate chloroform solution and a polyethylene glycol chloroform solution; dropping the mixed solution L into the mixed solution M to obtain a mixed solution N; dropping the mixed solution F into the mixed solution N to obtain a mixed solution O; dropping the mixed solution O into a polyvinyl alcohol solution to obtain a mixed solution P; adding the polyvinyl alcohol solution into the mixed solution P, then performing centrifugal separation, and freeze-drying to obtain the biodegradable multifunctional oil-absorbing particles capable of floating on the water surface. The preparation process disclosed by the invention is simple, and the prepared oil-absorbing particles have the nitrogen and phosphorus sustained release function, the function of adsorbing petroleum hydrocarbons and the biodegradability.