The invention relates to a preparation method used for an arc-shaped rotary solid wood stair beam, comprising the steps as follows: preparing solid wood small billets, secondary drying, colour separating and material selecting, material cutting, finger jointing, four-surface plane forming, thin sheet cutting, plate assembling, precise saw width-fixing, sanding thickness-fixing, explosive-proof trough cutting on single plate, assembling and forming; the assembling and forming comprise the steps as follows: 1: a die is firstly adjusted; 2: step (height and width of step) of the stair is determined; 3: the single plate is fixed; 4: when the layer number required by the stair and the thickness of the beam are achieved, the die is locked and pressurized. The stairs produced according to the invention have good stability and no rebounce, are not easy to deform, have smooth and graceful whole lines meeting the requirement of decoration, have high bearing strength, are firm and reliable, have strong impact force resistance, ensure the safety, have high preciseness of the ladder radian, can be adjusted according to the requirement, can be produced industrially and have quick effect.