The characterization of chaotic convention and morphology of primary phase are mainly researched in different semisolid rare-earth La and Yb of A356 alloy under the different time and frequencies of electromagnetic field. The trajectories of the particle in semisolid A356 alloy melt are simulated by the computational fluid dynamics software Fluent,and the results of Kolmogorov entropy are calculated. The results show that Kolmogorov entropy is higher accompanied by the increasing frequencies and time. Combined with experiments,the primary phase in A356 semisolid is effected by the two same contents rare-earth at different stirring frequencies and time. The morphologies of primary phase are both observed better than stirred for 15 s at 30 Hz,meanwhile,the morphology of A356-Yb primary phase is observed better than A356-La primary phase. Through the simulation and experiment,random chaos imply the rules,the morphology of primary phase is effected by added rare-earth,electromagnetic stirring frequencies and time.