In order to meet the requirements of light weight， high strength and near net forming of a complicated aerospace component， an isothermal superplastic forward and backward extrusion near net forming method based on thin-walled component of low-density Mg-Li alloy was proposed. The formability of as-cast and the mechanical properties of as-cast and as-rolled at different temperatures were studied. The results show that the elongation of as-cast is about 12%， and the tensile strength is about 145 MPa. The elongation of as-rolled has little change， but the tensile strength increases to more than 180 MPa. The elongation and tensile strength obtained by this method are significantly improved， reaching 21% and 216 MPa， respectively， which indicates that the grain refinement is realized in the process of high temperature and large deformation. While many reinforcement phases are dispersed in the grain， which plays the role of performance enhancement. The performance enhancement and precision forming of complicated structural parts are successful achieved.