A cooling medium control method for a multi-connected air conditioning system, the multi-connected air conditioning system comprising a compressor, an outdoor unit, and a plurality of indoor units connected to the outdoor unit, the outdoor unit comprising an outdoor expansion valve, and each of the indoor units comprising an indoor expansion valve; wherein the cooling medium control method comprises the following steps: S 110. acquiring current operating values of target parameters of the compressor during the operation of the compressor; S 120. calculating deviation degrees of the target parameters of the compressor according to the current operating values of the target parameters of the compressor and standard operating ranges of the target parameters of the compressor; and S 130. selectively adjusting an opening degree of the outdoor expansion valve or the indoor expansion valve based on the deviation degrees; and wherein the standard operating ranges of the target parameters are operating ranges of the target parameters specified by a normal operating state of the compressor, characterized in that in step S110, the target parameters comprise a high pressure of the compressor, and the current operating value of the high pressure is Pd; and in step S120, when Pd lower limit ≤Pd≤Pd upper limit, a deviation degree D pd of the high pressure Pd is 0; when Pd>Pd upper limit, the deviation degree D pd of the high pressure Pd is calculated according to the following formula: D pd =Pd upper limit /Pd-1; and when Pd<Pd lower limit, the deviation degree D pd of the high pressure Pd is calculated according to the following formula: D pd =Pd lower limit /Pd-1; wherein Pd upper limit is a maximum value in the standard operating range of the high pressure, and Pd lower limit is a minimum value in the standard operating range of the high pressure. S 110. acquiring current operating values of target parameters of the compressor during the operation of the compressor; S 120. calculating deviation degrees of the target parameters of the compressor according to the current operating values of the target parameters of the compressor and standard operating ranges of the target parameters of the compressor; and S 130. selectively adjusting an opening degree of the outdoor expansion valve or the indoor expansion valve based on the deviation degrees; and wherein the standard operating ranges of the target parameters are operating ranges of the target parameters specified by a normal operating state of the compressor, characterized in that in step S110, the target parameters comprise a high pressure of the compressor, and the current operating value of the high pressure is Pd; and in step S120, when Pd lower limit ≤Pd≤Pd upper limit, a deviation degree D pd of the high pressure Pd is 0; when Pd>Pd upper limit, the deviation degree D pd of the high pressure Pd is calculated according to the following formula: D pd =Pd upper limit /Pd-1; and when Pd<Pd lower limit, the deviation degree D pd of the high pressure Pd is calculated according to the following formula: D pd =Pd lower limit /Pd-1; wherein Pd upper limit is a maximum value in the standard operating range of the high pressure, and Pd lower limit is a minimum value in the standard operating range of the high pressure.