Abstract: The effects of explant selection, high osmotic treatment, co-culture with Agrobacterium, screening of transformed plants by selecting medium on the callus growth and transformation efficiency were studied in the process of maize transformation mediated by Agrobacterium. The results show that the growth rate and transformation efficiency of immature embryos derived from a vigorous ear are higher than those from other ears.High osmotic treatment and co-culture with Agrobacterium and herbicide screening impede the callus growth. The solutions are put forward.