The present invention relates to a method for calculating loading amount of ammonia in a selective catalytic reduction apparatus, which may include: detecting a change amount of temperature in the selective catalytic reduction apparatus; determining whether the change amount of temperature in the selective catalytic reduction apparatus increases; calculating a loading modification amount of ammonia according to the change amount of temperature if the change amount of temperature in the selective catalytic reduction apparatus increases; calculating a loading change amount of ammonia based on the calculated loading modification amount of ammonia; calculating a current loading amount of ammonia based on the calculated loading change amount of ammonia; and dosing the current loading amount of ammonia into the selective catalytic reduction apparatus.