The iaaM, a tryptophan monooxygenase gene deriving from bacteria, can catalyze the synthesize of indole acetic acid (IAA) with tryptophan via indoleacetamide pathway in plants. A trichome specific expression of iaaM vector by recombination of the trichome specific GL2 gene promoter of Arabidopsis and iaaM gene coding region was constructed. The recombinant was transformed into tobacco WS38 by Agrobacterium tumefaciens mediated leaf disc transformation and 6 transformed tobacco plantlets were screened and identified. A comparative experiment was transformation of Arabipdopsis by the Agrobacterium tumefaciens infiltration method with the same recombinant and 9 transformed seedlings were screened out. A systematic observation of the epidermal trichome of stably transformed transgenic plants showed that the trichome of transgenic tobacco grew significantly longer than those of control plants with the length 2.2 times than that of the control. However, there was no significant increase in the length of trichome in transgenic arabidopsis. The IAA content in young leaf of the iaaM transgenic tobacco was significantly increased indicating that iaaM was expressed in tobacco trichome cells so that it achieved more auxin synthesis and accumulation in trichome cells. It was interesting that there was a significant increase in trichome density both in transgenic Arabidopsis and tobacco. It might existed a more complex correlation between the specificity of the GL2 promoter expression in trichome determination and the auxin homeostasis. The mechanism of the trichome elongation in transgenic tobacco was also deduced.