The invention belongs to the technical field of automatic control over thermal power generating units, and particularly relates to an automatic control optimization method for a primary air fan of a thermal power generating unit. The automatic control optimization method can be used for automatic control over the primary air fan in the actual operation process of the thermal power generating unit,and guarantees that in the operation process of the unit, hot primary air mother tube pressure is automatically controlled to be within a reasonable range. Hot primary air mother tube pressure set value control logic, hot primary air mother tube pressure PID regulator feedforward control logic, hot primary air mother tube pressure PID regulator upper limit and lower limit control logic, primary air fan over-current protection control logic and primary air fan anti-stall automatic control logic are added in the control logical configuration of a thermal power generating unit distributed control system (DCS), correct actions of primary air fan guide vanes are controlled, the primary air mother tube pressure is automatically controlled to be within the reasonable range, and the pulverizing output requirement is met. Through the existing unit DCS coordinate control system, the real-time performance is good, the field debugging process is simple, and engineering implementation is facilitated.