The invention discloses a corn straw yellow silage synergist which is prepared from the following components in parts by weight: 50-70 parts of jerusalem artichoke, 35-45 parts of fritillaria powder,25-35 parts of rhizoma atractylodis, 4-8 parts of indigo naturalis, 30-38 parts of white spiral shell, 0.01-0.05 part of a lactic acid bacteria preparation, 0.003-0.006 part of an enzyme preparation,and 0.002-0.005 part of a sugar preparation. The enzyme preparation includes amylase, cellulase, hemicellulase, dextranase and glutamine transaminase. The sugar preparation includes fructose, ethyl maltol, disodium inosinate and potassium sodium tartrate. The prepared corn straw yellow silage synergist can shorten the fermentation time of corn straw to 3-5 days, can effectively reduce the use amount of a fermentation agent, can improve the quality of corn straw yellow silage, reduces the pH value of fermentation products and increases the lactic acid content.