The invention relates to a preparation method of cellulase, which comprises the following steps: (1) preparing liquid strain in a culture vessel; (2) culturing mother culture in a triangular flask; (3) performing solid thick-layered ventilation fermentation culture of the strain; and (4) refining and purifying the strain. The invention prepares high energetic cellulase by preparing the liquid strain and performing the solid thick-layered ventilation fermentation culture, and the enzyme activity can reach more than 90,000 IU/g on the premise of not increasing the production cost.