TECHNOLOGY FOCUS - BIOLOGY - Preferred Components: The yeast in step (d) is yeast BY4742.    TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Components: The nutrient solution in step (d) includes (in g/l) potassium dihydrogen phosphate (0.07), magnesium sulfate monohydrate (0.035), calcium chloride (0.01), sodium chloride (0.01), manganese sulfate tetrahydrate (011), copper sulfate pentahydrate (0.2), zinc sulfate heptahydrate (2.1), cobalt sulfate monohydrate (0.42 and ferrous sulfate (1.44).    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Method: The rotating speed of centrifuge in step (b) is 4000 revolutions/minute, the centrifugal time is 15 minutes, the liquid supernatant after centrifuging can be repeatedly used after adding sodium hydroxide. The straw deposit of step (b) is washed with distilled water until the liquid supernatant after centrifuging is neutral. The stirring speed of stirring and hydrating is 250 revolutions/minute. The pH value of 4.5 in step (c) is controlled by: placing the mixture of straw powder and cellulose in a hydrating tank, where the hydrating tank is provided with a pH electrode and a pH control box connected to the pH electrode to monitor online, and control the pH change in the hydrolysate; setting the pH value as 4.5 plus minus 0.05 by the pH control box; controlling the acid and alkali peristaltic pump to automatically feed dilute hydrogen chloride or dilute sodium hydroxide solution by the pH control box; and controlling the pH value of hydrolysate within the set scale, where the rotating speed of peristaltic pump is 1 revolutions/minute, the concentrations of dilute hydrogen chloride or dilute sodium hydroxide solution are 0.5 mol/l. The control of pH value in constant-temperature fermenting process of step (d) includes: providing the hydrating tank with a pH electrode, and a pH control box connected to the pH electrode to monitor on-line, and control the pH change in the hydrolysate; setting the pH value by the pH control box as 4.5 plus minus 0.05; controlling the acid and alkali peristaltic pump to automatically feed dilute hydrogen chloride or dilute sodium hydroxide solution by the pH control box; and controlling the pH value of hydrolysate within the set scale, where the rotating speed of peristaltic pump is 1 revolutions/minute, the concentrations of dilute hydrogen chloride or dilute sodium hydroxide solution are 0.5 mol/l.