The invention discloses liquid fuel based on combustible organic wastes and a preparation method of the liquid fuel. The liquid fuel comprises a polymer waste fraction, oil sludge, coal and an additive, wherein the additive is capable of achieving effects of stable viscosity and high sedimentation stability; the additive comprises carbonate minerals and a plasticizer; the carbonate minerals comprise one or several of sodium carbonate, calcium carbonate, trona or calcite; the plasticizer comprises sodium lignin sulfonate. The fuel can still maintain high rheological property while ensuring thata heat value of the liquid fuel is obviously improved, the cost of the liquid fuel is reduced, and the environmental safety is improved. The fuel is environmental safety type liquid fuel which can beapplied to production pipeline transportation and can be directly burned by virtue of a boiler nozzle.