NOVELTY - Dried corn straw is crushed, pretreated, and uniformly mixed and placed in environment sealed. Then, acidification of pretreated corn straw is carried out by using semi-continuous feed methane phase as inoculum, and pH is measured every day. When the pH is less than 5.5, acidification is terminated and semi-continuous methanation is started in a stirred tank of anaerobic reactor with reaction volume of 8 L by adding 120 g anaerobic sludge to the reactor, then adding 520 g pretreated corn straw and terminating methanation reaction when pH reaches 7.    USE - Method of improving performance of anaerobic digestion gas during methanation discharge pretreated corn straw acidification (claimed).    ADVANTAGE - The method efficiently and economically improves performance of anaerobic digestion gas during methanation discharge pretreated corn straw acidification by reducing acidification time and strengthening the stability of the anaerobic system.    DETAILED DESCRIPTION - Dried corn straw is crushed to size of 20 mesh or less, pretreated using water with content of 6 times the dry weight of corn straw as pretreatment agent, and uniformly mixed and placed in environment sealed at 40 plus minus 20 degrees C for 1 day. Then, acidification of 52 g pretreated corn straw is carried out by using 100-700 mL semi-continuous feed methane phase with dry mass of 55% as inoculum after adding water to 80% of the total volume of the reaction vessel, uniformly mixing, purging with nitrogen, then sealing with a rubber stopper and securing in blue cap bottle shaker and shaking at 40 plus minus 20 degrees C, and pH is measured every day using a pH meter. When the pH is less than 5.5, acidification is terminated and semi-continuous methanation is started in a stirred tank of anaerobic reactor with reaction volume of 8 L by adding 120 g anaerobic sludge to the reactor, then adding 520 g pretreated corn straw, then adding water to 80% of total volume, filling with nitrogen, setting the reactor temperature to 35 plus minus 2 degrees C and terminating methanation reaction when pH reaches 7.