The invention relates to an SCR feedforward control calculation method. The method comprises the following steps that the SCR efficiency urea jet amount is determined and obtained according to the air speed, the SCR average temperature, the NO2/ NOx ratio, the NOx mass flow and the urea concentration; the ammonia-nitrogen ratio urea jet amount is determined according to the urea concentration, the NO2/ NOx ratio, and the NOx mass flow to be converted; the urea jet amount after ammonia oxidation modification is obtained by multiplying the ammonia-nitrogen ratio urea jet amount by the ammonia oxidation factor; the urea jet amount of a fresh catalyst in the steady state is obtained by comparing the ammonia oxidation modified urea jet amount with the SCR efficiency urea jet mount and selecting the smaller value of the urea jet amount after ammonia oxidation modification and the SCR efficiency urea jet amount; and the feedforward urea jet amount is obtained by multiplying the urea jet amount of the fresh catalyst in the steady state by the transient modifying factor and the aging modifying factor. According to the method, the real-time and accurate control over the feedforward urea jet amount is achieved, and the difficulty of subsequent feedforward control adjustment of the urea jet amount is greatly reduced.