Abstract: A use of an application mode of Trichoderma harzianum (T. harzianum) in growth and induced resistance of Nicotiana tabacum (N. tabacum) includes the following specific operation steps: S1. experimental materials: preparation of test media and bacterial solutions; S2. experimental treatments: S2.1 control treatment; S2.2 seed soaking treatment; S2.3 root irrigation treatment; and S2.4 foliar inoculation treatment; S3. test determination indexes and methods: S3.1 determination of biological traits; S3.2 determination of physiological and biochemical indexes; and S3.3 determination of disease resistance and induced resistance indexes; and S4. data processing: subjecting data to a difference significance test. Different application modes of T. harzianum all can promote the growth of N. tabacum plants and reduce the occurrence of tobacco black shank (TBS), among which a root irrigation treatment at a transplanting stage leads to an optimal effect.