The invention discloses a pretreatment method for preparation of biomass fuels by comprehensive utilization of all components of plant straw, and relates to the field of comprehensive utilization of all components of plant straw, wherein the pretreatment method comprises the steps: plant straw after being cut into sections is successively subjected to washing treatment for two times before and after steam explosion, steam explosion treatment, extrusion treatment, crushing treatment, pre-enzymolysis treatment, cracking treatment, and enzymolysis treatment, and finally a pre-product for preparing the biomass fuels is obtained; a straw washing liquid obtained after washing treatment and an extrusion liquid obtained after extrusion treatment are used for producing marsh gas, and a liquid, gas and solid biomass fuels can be obtained after the pre-product is treated. The method realizes separation and high-valued complete utilization of the all components of the plant straw, namely hemicellulose, cellulose, lignin and a small amount of components, can achieve no pollutant emission, and has the advantages of easy industrialization operation, good economic benefits, and remarkable comprehensive social benefits.