TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Method: The wheat stalk is cleaned and naturally dried, and then is cut into small pieces having length of 2-3 cm. The ammonia pre-processing comprises mixing wheat stalk with urea solution having concentration of 30-50 g/l according to mass of wheat stalk to volume of urea solution of 50 g:200 ml, sealing and processing at temperature of 30 degrees C. The sealing step comprises processing for 25 days at temperature of 30 degrees C. The completely mixed anaerobic fermentation comprises: placing the ammonia pre-processed wheat stalk in an extraction and fermentation tank, regulating ratio of carbon to nitrogen of 20:1-30:1, adding inoculum which is 30% by mass of total fermentation liquor in the extraction and fermentation tank, regulating initial pH value to 7, and placing in a thermostatic water bath and performing anaerobic fermentation. The step of regulation of ratio of carbon to nitrogen comprises regulating with ammonium bicarbonate. The step of regulation of initial pH value to 7 comprises regulating initial pH value to 7.0 with 5 mole/l of hydrochloric acid. The thermostatic water bath is thermostatically stirred at temperature of 38 degrees C, and at a stirring speed of 100 rotations per minute. The anaerobic fermentation time is 25 days. The inoculum is active sludge which is fermented residue from normally fermented methane system. EXAMPLE - Raw wheat straw material was cleaned and dried under the natural condition and was cut into 2 to 3 cm small sections. The raw material was put into a plastic barrel, and urea solution (30 g/l) was added to the barrel. Then the plastic barrel was covered with a plastic wrap insulating cover. The barrel was maintained for 25 days at a temperature of 30 degrees C. The ammonia pre-processed wheat stalk (48 g) was added to a fermentation device, an inoculum containing myelin oligodendrocyte glycoprotein and distilled water ware added to the fermentation device, where the mass of the total fermentation liquid is 800 g. The ratio of carbon to nitrogen of the fermentation liquid was regulated to 20:1. The initial pH value of the fermentation liquid was adjusted to 7 using 5 mole/l of hydrochloric acid. The fermentation device was sealed to ferment, and was in the constant temperature water bath The anaerobic fermentation was performed for 25 days, the temperature was controlled at 38 degrees C, and the fermentation device was connected with the drainage device, and continuously stirred at a stirring speed of 100 rotations per minute and worked up to give methane.