The invention discloses a biomass charcoal-based controlled release fertilizer with an insecticidal function and a preparation method thereof. The biomass charcoal-based controlled release fertilizer is characterized by taking rice straw, urea, kaolin, itaconic acid, acrylamide, ammonium ceric nitrate, attapulgite, N,N'-methylene bisacrylamide, bentonite, humic acid, zeolite, bacillus, 2-aminoethyl mercaptan hydrochloride, dimethyl cyanoamino di-tyiocarbonate, potassium carbonate, 2-chloro-5-chloromethyl thiazole and the like as raw materials. By taking the ammonium ceric nitrate as an initiator and taking the N,N'-methylene bisacrylamide as a cross-linking agent, the itaconic acid and the acrylamide are subjected to graft copolymerization to prepare composite super absorbent resin with good water retention capacity; the bentonite can be used to improve a soil structure and enhance water retention and drought resisting capability and fertility retaining and enhancing capability of soil; the composite super absorbent resin is compounded with the humic acid, the zeolite and the bacillus to prepare a soil conditioner which can be used to regulate a soil pH value, buffer a soil value and further increase crop yield.