The invention discloses a component detection and ammonia spraying control system of an SCR denitrification process. The component detection and ammonia spraying control system comprises an ammonia spraying main pipe, a plurality of ammonia spraying branch pipes, a flow field distribution controller and a smoke detection device, wherein the smoke detection device comprises a plurality of sampling heads which are arranged at an inlet flue and/or outlet flue of an SCR reactor, the plurality of sampling heads are distributed at different positions on the cross section of the inlet flue and/or outlet flue so as to detect the gas component data at different positions of the inlet flue and/or outlet flue, and the smoke detection device transmits the collected gas component data to the flow field distribution controller; and the plurality of ammonia spraying branch pipes are communicated with the ammonia spraying main pipe, and the openness of a valve of the ammonia spraying main pipe and the openness of a valve of each ammonia spraying branch pipe are controlled by the flow field distribution controller according to the gas component data. The total ammonia gas injection amount of the SCR reactor and the total ammonia gas injection amount of each ammonia spraying branch pipe are precisely controlled, so that the amount of the ammonia gas sprayed from the flues are reasonably re-distributed according to the concentration value of the harmful gas component measured by the smoke detection device in different areas of the flue.