Method for preparing compound fertilizer by straws

The invention particularly provides a method for preparing a compound fertilizer by straws. The method includes the steps of cutting the straws into sections, stacking the straw sections in a fermenting vat, adding an organic matter decomposition agent, and covering the fermenting vat with an environment-friendly degradable plastic film or mud to seal the fermenting vat; subjecting biogas obtained from fermentation to decontamination and purification, and delivering the decontaminated and purified biogas to homes of residents to be used for combustion or/and to be used for production or/and to be stored; subjecting biogas residues and biogas liquid to separation, taking the biogas residues to be used or stored as a pollution-free organic total-nutrient solid fertilizer, and taking the biogas liquid to be used or stored as a pollution-free organic total-nutrient liquid fertilizer; during use, using the solid fertilizer and the liquid fertilizer in a separate or a mixing manner. The method for preparing the compound fertilizer by the straws has the advantages that the produced compound fertilizer is high in nutrition content, the defect that the straws in rural areas cannot be treated and are burned is avoided, the organic fertilizer manufactured by the aid of the straws is beneficial to absorption of plants, and the fertilizer manufactured by the method is wide in usage range.