The formability of the magnesium alloy sheets is poor at room temperature even though the magnesium alloy sheets are attractive because of their excellent characteristics. Hydro-forming technology, especially the pulsating hydro-forming, may be a way to improve the formability. Finite element simulations have been conducted to investigate the formability of AZ31B magnesium alloy sheet in hydro-bugling by pulsating hydraulic pressure. The influence of linear pressure, pulsating pressure and pulsating frequency on the maximum bulging height and minimum wall thickness of the formed parts have been analyzed. The research results show that the formability of AZ31B magnesium alloy sheet can be improved dramatically by pulsating hydro-forming. And enough bugling height can be obtained by lesser forming hydraulic pressure. The AZ31B sheet has an excellent performance in formability when the pulsating frequency is properly selected.