The present invention provides an AC microgrid economical operation control method and a device. The method comprises the following steps of for any distributed power supply in an AC microgrid, acquiring the optimal active power function of the distributed power supply; when the optimal active power function is continuous and derivable within the closed interval of a required active power variation range and is an increment function, acquiring the reference frequency of the distributed power supply based on the active power outputted by the distributed power supply and the inverse function of the optimal active power function; based on the reference frequency of the distributed power supply, adjusting an inverter corresponding to the distributed power supply. According to the technical scheme of the invention, based on the AC microgrid economical operation control method, when the AC microgrid is in a steady state, each distributed power supply can provides the active power for a load according to the optimal active power. That means, the active power is provided for the load at a lowest power generation cost, so that the purpose of the optimal economic operation is realized.