The invention relates to a method for preparing a medical porous NiTi shape memory alloy by microwave sintering. The method comprises the following steps of: (1) compounding powder: compounding titanium powder, nickel powder and pore-forming agent powder according to certain mass percentage; (2) performing ball milling: putting the compounded powder body into a stainless steel ball milling pot for ball milling; (3) pressing billets: performing mold pressing on the powder materials after the ball milling at the pressure of between 50 and 500 MPa into pressed billets; (4) charging in a furnace:putting the obtained pressed billets and a microwave auxiliary heating material into a polycrystalline mullite fiber heat insulation barrel, and putting the heat insulation barrel into a microwave sintering furnace; and (5) performing microwave sintering. The method has the advantages that: the preparation method is simple and convenient, the sintering cycle is short, the energy consumption is low, the method is suitable for industrialized production, the porous NiTi shape memory alloy obtained by sintering has good mechanical properties, a pore structure is in three-dimensional communication, the pore ratio is controllable between 20 and 80 percent, the pore sizes are uniform and are controllable between 30 and 600 mu m, and the medical porous NiTi shape memory alloy can be used as materials for repairing and replacing hard tissues such as bones, joints, artificial tooth roots and the like.