Effects of holding time and temperature on the microstructure and size as well as morphology of primary phase in AM60B alloy during semi-solid isothermal treatment process were investigated. The results show that during semi-solid isothermal treatment, eutectic phase with net-like structure is prior to be melt, and then α phase is melt and separated to that to convert into globular particles with increasing in holding time. However, spheroidal particle can be coalesced with further increasing in holding time, where coalescence of the grain becomes more and more serious with increasing in holding temperature. The experimental results reveal that spheroidized non-dendrite phase in the AM60B alloy can be observed with isothermal treatment at 595℃ for 60⁷5 min. Two-steps techniques can promote the formation of non-dendritic structure and contribute to get more and fine non-dendrite .