A method for controlling a multi-split air conditioner. The method includes detecting whether the degree of superheat of each outdoor unit meets a target requirement, if yes, determining whether a difference between an average exhaust temperature of each outdoor unit and an average exhaust temperature of an outdoor unit system reaches a preset value, if yes, comparing the size of the average exhaust temperature of each outdoor unit with the size of the average exhaust temperature of the outdoor unit system, according to the result between the size of the average exhaust temperature of each outdoor unit and the size of the average exhaust temperature of the outdoor unit system, controlling an electronic expansion valve to actuate to make the average exhaust temperature of each outdoor unit to approximate to the average exhaust temperature of the outdoor unit system.