A method for controlling a multi-split air conditioning system, comprising: acquiring an outdoor ambient temperature when receiving a starting instruction of an indoor unit; determining whether the outdoor ambient temperature is within a preset temperature range; and determining an operating mode of the multi-split air conditioning system according to operating conditions of respective started indoor units, when the outdoor ambient temperature is within the preset temperature range, the method being characterised by further comprising: determining the operating mode of the multi-split air conditioning system according to the operating conditions of respective started indoor units when the outdoor ambient temperature is within the preset temperature range comprises: determining whether there is a started indoor unit, when the outdoor ambient temperature is within the preset temperature range; determining whether the indoor unit sending the starting instruction has a highest priority level, when there is the started indoor unit; and determining the operating mode of the multi-split air conditioning system according to an operating mode set by the indoor unit sending the starting instruction when the indoor unit sending the starting instruction has the highest priority level, and determining the operating mode of the multi-split air conditioning system according to the operating mode of the started indoor unit when the indoor unit sending the starting instruction does not have the highest priority level. acquiring an outdoor ambient temperature when receiving a starting instruction of an indoor unit; determining whether the outdoor ambient temperature is within a preset temperature range; and determining an operating mode of the multi-split air conditioning system according to operating conditions of respective started indoor units, when the outdoor ambient temperature is within the preset temperature range, the method being characterised by further comprising: determining the operating mode of the multi-split air conditioning system according to the operating conditions of respective started indoor units when the outdoor ambient temperature is within the preset temperature range comprises: determining whether there is a started indoor unit, when the outdoor ambient temperature is within the preset temperature range; determining whether the indoor unit sending the starting instruction has a highest priority level, when there is the started indoor unit; and determining the operating mode of the multi-split air conditioning system according to an operating mode set by the indoor unit sending the starting instruction when the indoor unit sending the starting instruction has the highest priority level, and determining the operating mode of the multi-split air conditioning system according to the operating mode of the started indoor unit when the indoor unit sending the starting instruction does not have the highest priority level. determining whether there is a started indoor unit, when the outdoor ambient temperature is within the preset temperature range; determining whether the indoor unit sending the starting instruction has a highest priority level, when there is the started indoor unit; and determining the operating mode of the multi-split air conditioning system according to an operating mode set by the indoor unit sending the starting instruction when the indoor unit sending the starting instruction has the highest priority level, and determining the operating mode of the multi-split air conditioning system according to the operating mode of the started indoor unit when the indoor unit sending the starting instruction does not have the highest priority level.