The invention provides a compound microorganism bacterium agent for a banana stem and leaf silage and a preparation method of the compound microorganism bacterium agent. The preparation method comprises the following steps: A, preparing a lactobacillus plantarum freeze-dried bacterium agent; B, preparing freeze-dried candida utilis; C, preparing freeze-dried tannase; D, reviving the lactobacillus plantarum freeze-dried bacterium agent, the candida utilis and the tannase in sequence; E, fully stirring the obtained revived bacterium agents to prepare revived water, wherein the bacterium content of the revived water is kept at 10<8>-10<10> cfu/mL; F, cutting banana stems and leaves into pieces with size of 2-4 cm, processing until the water content is about 60-65 percent, uniformly stirring the revived water obtained in the step E and the banana stems and leaves, holding in a fermentation tank, compacting, sealing and keeping out of the sun at normal temperature to prepare the banana stem and leaf silage. By using the method, the waste material can be changed into things of value, tannin which goes against digestion in the banana stems and leaves can be eliminated and passivated, the cellulose content is reduced, the high-quality silage is developed, and great economic benefit is produced.