The invention relates to a method for determining the inlet parameter of an SCR denitration device. According to the method, a boiler furnace, a horizontal flue and a tail portion flue are used as calculating objects, numerical simulation of the total-system combustion, heat transfer and flowing process is conducted by the aid of Fluent software, the flue gas parameters of an economizer outlet, namely an inlet of the SCR denitration device under different working conditions are obtained, and the flue gas parameters relate to velocity distribution, temperature distribution and smoke component concentration distribution; according to the whole system from the boiler furnace, the horizontal flue and the tail portion flue (to the economizer outlet), numerical simulation of the combustion, heat transfer and flowing process is conducted, movement of solid-phase particles is also taken into account, the solid-phase particle parameters of the economizer outlet, namely the inlet of the SCR denitration device under different working conditions are obtained, the problems that the design calculation and engineering actual deviation of the SCR denitration device is too big due to the fact that the inlet flue gas parameter cannot be reasonably set traditionally, and catalyst abrasion and dust accumulation can be caused for giving too little care to the movement of solid-phase particles are solved, hence, the denitration efficiency of an SCR reactor can be effectively improved, and the service life of catalysts is prolonged.