A process of warm deep drawing of magnesium alloy with variable blank holder force has been presented in this study. A hydraulic press that can realize adjustable blank holder forces was developed and its working principle and control system introduced. A warm deep drawing mould was fixed and warm deep drawing experiments are conducted on the hydraulic press. Different variation schemes of the blank holder force with the stroke of the punch was tested, and compared with experiment results. The experimental results show that adopting the variable blank holder force technique can remarkably improve the forming performance and decrease the reduction ratio of thickness from 15.21% to 12.35%. It is further demonstrated that the suitable blank holder force variation scheme is an inverted V curve with the punch stroke.