Abstract: Ulmus pumila is one of the important native species in China. In order to promote artificial hybrid cultivation and selection of polyploid Ulmus pumila in our country. Using diploid, triploid and homologous tetraploid Ulmus pumila leaves as test materials, the phenotypic indexes, microscopic differences and photosynthetic physiological characteristics of leaves were measured.The degree of variation among different ploidy and the effect of gene ploidy change on Ulmus pumila were compared and analyzed. The results showed that the leaf length, leaf width and leaf area of triploid and homologous tetraploid Ulmus pumila were significantly higher than those of diploid Ulmus pumila. It can be seen that the morphological characteristics of Ulmus pumila such as leaf length, leaf width and leaf area showed magnification after multiploidy. The thickness of upper and lower epidermis, palisade tissue and spongy tissue of leaves of tetraploid and triploid Ulmus pumila were higher than those of diploid Ulmus pumila, and the characteristics of magnification were very prominent.Under the same magnification field, the ploidy increased the sparse density of stomatal apparatus, this showed there was obvious correlation between stomatal density and ploidy. The Pn and Tr of triploid and homologous tetraploid Ulmus pumila were significantly higher than those of diploid Ulmus pumila, so the increase of ploidy would increase the Pn and Tr of Ulmus pumila. The content of Chl a was higher than that of Chl b, and the contents of Chl a, Chl b and Chl increased with the increase of ploidy.It showed obvious characteristics of photosynthetic pigment content in polyploid plants.