Trichoderma harzianum is a well-known biological control agent (BCA) that is effective against a variety of plant pathogens. We had found through previous studies that the Trichoderma harzianum T4 can effectively control a variety of plant pathogens. In order to further investigate the mycoparasitism mechanism of T. harzianum T4, transcriptomic sequencing were used to identify the differentially expressed genes (DEGs) of T. harzianum T4.