In order to clarify the taxonomic value and systematic significance of leaf epidermal trichomes characters， the leaf epidermal trichomes of 33 species of Populus in China were observed and analyzed by stereomicroscope and scanning electron microscope. The results showed that Trichomes of Populus were overall non-glandular， simple， basally fixed； and all species except P. euphratica were covered with trichome in leaf epidermis， but the distribution， appearance， and length of the trichomes varied to different degrees among species. The shape of the trichomes（cylindrical to striped）， the degree of curvature（erect to curled）， the orientation relative to the surface of the leaf epidermis（ambulatory or not）， and the length of the trichomes were of taxonomic significance. Combined with the evolutionary framework provided by molecular phylogenetic studies， this study concluded that leaf epidermal indumentum characters of Populus were difficult to distinguish at the subgeneric level， the leaf trichomes within subg. Tacamahaca were similar and stable， but the length of leaf trichomes on different branches was different， however， many species could be distinguished between subg. Turanga and subg. Populus. Leaf trichomes characters could be divided into the following types after the integration of characters： glabrous， felted， sericeous， pubescent and villous.