A method of calculating power consumption of an air conditioner is provided. The method includes calculating, b a controller, a parameter of an autoregressive moving-average (ARMA) model using past initial temperature and target temperature data of an air conditioner as an input variable of the ARMA model, and past accumulated power consumption data of the air conditioner as an output variable of the ARMA model. The controller is configured to set a current target temperature of the air conditioner and detect an indoor temperature of a vehicle, in which the air conditioner is installed. In addition, the controller is configured to substitute the current target temperature, the indoor temperature, and the parameter to the ARMA model, and predict current accumulated power consumption of the air conditioner.