In this paper, effect of Ca on hot deformation behavior and workability of Mg-Gd-Y-Zn-Zr alloy were investigated by Gleeble 3500 thermal simulation tester conducted at a temperature ranging from 573K to 723K and strain rate varying from 0.001s-1 to 1s-1. It’s indicated that the addition of Ca increased the flow stress and hot deformation active energy, widened the range of processing stable zone and the optimal processing zone, but decreased the maximum power dissipation efficient, and inhibited the dynamic recrystallization. Combined the microstructure after thermal compression which was analyzed by laser confocal microscopy, the accuracy of the processing map was verified. The optimized hot processing parameters of Mg-Gd-Y-Zn-Zr were formulated, namely strain rate ranging from 0.001s-1 to 0.01s-1, temperature ranging from 623K to 723K. Depending on the optimum processing parameters, an isothermal forged magnesium alloy with good quality and no deformation defects was fabricated.