The invention provides a whole-working-condition flue gas denitrification and air preheater anti-blocking system, belonging to the field of coal-fired boilers. The system solves the problems of high implementation cost of the existing whole-working-condition flue gas denitrification and air preheater anti-blocking system and large modification to the original system, and comprises a furnace, an air preheater, a denitrification device and a secondary air duct, wherein a secondary air channel and a flue gas channel are arranged on the air preheater, the secondary air channel is positioned on thesecondary air duct, the outlet of the secondary air duct is connected with the inlet of the furnace, the secondary air duct is sequentially provided with an auxiliary heating device and an adjustingmember I in the air outlet direction, the adjusting member I is located between the auxiliary heating device and the secondary air channel, the system further comprises a bypass line connected with the secondary air channel and communicates with the inlet of the furnace, the joint between the bypass line and the secondary air duct is located between the adjusting member I and the auxiliary heatingdevice, and the bypass line is provided with an adjusting member II. The system has the advantages of wide applicability, simple scheme, low implementation cost and the like.