The invention discloses an automatic control system for air volume and the air pressure of a thermal power generating unit. The system is characterized in that air pressure control is carried out through fans and baffles, frequency conversion control is carried out by combining a blower, the fans and the baffles are almost completely opened under a high load, the opening degree under a low load isgreatly improved, the wind resistance of the baffles is reduced, the number of actions of the baffles is effectively reduced, and the reliability and the service life of the baffles are improved. Bymeans of the air blower variable-frequency automatic control and air pressure cooperative control scheme, the air pressure fed into a hearth by the blower under the current load can be obtained, the speed of controlling an induced draft fan according to the negative pressure of the hearth is increased, the automatic control of the air volume and the air pressure of the thermal power generating unit is realized, the throttling loss of the system is reduced, and the surge phenomenon of the fans is reduced. A automatic starting and stopping system of the air blower is added, the optimal frequencyconverter instruction and the operating number of units of the fans are calculated according to the current load and the power consumption characteristic curve of the fans, the optimal operation combination mode of the fans is judged, starting and stopping of the fans are automatically controlled, and the energy consumption of the system is reduced.