The invention provides a method for preparing gypsum-free Portland cement. The method comprises the following step: performing contact method pretreatment on the surface of a cement clinker by using mixed air flows, wherein the mixed air flows at least comprise vapor flows. According to the method, an inherent mode that curing of cement is adjusted by mixing general purpose Portland cement with gypsum is changed, granular fine powder of Portland cement clinker is pretreated by using a surface contact method, and thus a pretreatment product is generated and deposited on surfaces of tricalcium aluminate granules in minerals of the cement clinker; the cement clinker treated by using the method is mixed with a proper amount of mixed materials to prepare the gypsum-free Portland cement, when the cement is mixed with water, the pretreatment product deposited on the granule surfaces of the pretreated clinker is capable of effectively retarding the hydration speed at a later stage that the cement is mixed with the water, and effective adjustment on the curing velocity at a primary stage of the cement can be achieved; and both the hydration heat release velocity and the heat accumulation capacity of the gypsum-free Portland cement prepared by using the method are remarkably lower than those of ordinary Portland cement.