NOVELTY - A crop straw is used to prepare clean vehicle fuel by mixing crushed crop straw with sodium hydroxide, sodium sulfide, and water, and preserving in sealed container; mixing pre-treated crop straw with inoculation sewage and water, adding sodium hydroxide solution or hydrochloric acid solution to adjust pH value of system to 6.8-7.4, and anaerobic digesting to generate firedamp; introducing firedamp to absorbent solution, and removing carbon dioxide and hydrogen sulfide in the firedamp; and passing obtained gas through active carbon molecular sieve to eliminate impurity and water in the gas.    USE - Using crop straw to prepare clean vehicle fuel.    ADVANTAGE - The method is able to improve firedamp yield of crop straw anaerobic digestion and shorten gas producing period. It has low cost, uses simple equipment, and fits for industrialization production.    DETAILED DESCRIPTION - Using crop straw to prepare clean vehicle fuel involves:    (A) crushing crop straw; mixing crop straw with sodium hydroxide, sodium sulfide, and water at a weight ratio of 100:6:6:80; and preserving in sealed container for 30 days at normal temperature;    (B) mixing pre-treated crop straw with inoculation sewage and water, in which the crop straw is 65-80 g dry weight/l and the sludge is 15000 mg/l; a carbon nitrogen ratio of the added ammonium chloride adjusting system is 20-30:1; adding sodium hydroxide solution or hydrochloric acid solution to adjust pH value of system to 6.8-7.4; and anaerobic digesting at 35 degrees C to generate firedamp;    (C) introducing firedamp to absorbent solution at 30 degrees C; and removing carbon dioxide and hydrogen sulfide in the firedamp; and    (D) passing obtained gas through active carbon molecular sieve to eliminate impurity and water in the gas; passing purified gas through condensation; and canning to obtain the clean vehicle fuel.    An INDEPENDENT CLAIM is included for a device of performing the method of using crop straw to prepare clean vehicle fuel, comprising anaerobic digestion device (1), gas storage pot (4), absorbing tower (7), filter device (13), regenerating device (9), and liquid storage groove (11).    DESCRIPTION OF DRAWING(S) - The drawing is a schematic view of the device of performing the method of using crop straw to prepare clean vehicle fuel.    Anaerobic digestion device (1)    Gas storage pot (4)    Absorbing tower (7)    Regenerating device (9)    Liquid storage groove (11)    Filter device (13)