The quick plastic forming (QPF) behavior for fine-grained AZ91D magnesium alloy sheet with the thickness of 1.0 mm and the grain size of 6.0 µm was investigated. Free gas bulging tests were conducted under different gas pressure for 300 s in the range of 250-400°C to investigate how the temperature and pressure impact on the formability of QPF. Free gas bulging test results show that the bulge height of semisphere part exist the peak value of 33 mm under the gas pressure of 0.5 MPa at 400°C. QPF tests of cup part were performed based on the free gas bulging test results. A cup part with the height of 20 mm which both of surface quality and fillet radius were satisfactory was formed using a two-stage loading path at 400°C during 300 s. Furthermore the microstructural revolution law during the QPF was discussed. The larger the thinning rate of parts is, the smaller the grain size will be.