Twin roll casting method is a promising route to directly produce magnesium alloy strip. It is a rapid solidification process with high temperature gradient combined with thermal flow and rolling deformation in the casting region. As-cast strip with proper microstructure is requested to serve as next rolling feedstock. However the microstructure of as-cast strip is sensitive for casting conditions during the casting process and the as-cast microstructure greatly affects the mechanical properties. In this work,the effect of casting speed,pouring temperature,deformation as well as anneal process on microstructure and mechanical properties were investigated. The results revels that twin-roll casting process can effectively refine the grain size,improve the morphology and distribution states of Mg17Al12. The homogenization treatment time can be shorted for the fine microstructure and lower the cost dramatically for the next forming process.