Abstract: The callus induced from the hypocotyl in Medicago varia cv. Gannong No.1, was cultured in the UM medium supplied with the PEG6000 of various concentrations, NAA (0.1mg/L) and KT (0.5mg/L), to induce the somatic embryos. Then the study on effect of PEG6000 on the somatic embryogenesis and observation on cytological structure of embryo were carried out in this paper. The results show that, the regeneration medium with proper concentration of PEG6000 are advantageous to somatic embryogenesis, the highest frequency of somatic embryogenesis appeared in regeneration medium with 6%PEG6000; via observed the paraffin sections, we found forming a whole somatic embryo will go through four developing phases, heart-shape embryo, torpedo embryo and cotyledon-shape embryo.