A method and device for adjusting an oil volume of a compressor of a multi-split system. The method comprises the following steps: (S1) during an operation of a multi-split system, detecting at a first pre-set time interval whether an oil volume of a compressor is insufficient; (S2) if the oil volume of the compressor is insufficient, controlling an oil volume adjusting unit to turn on for a second pre-set time and then turn off; (S3) acquiring a total turn-on time of the oil volume adjusting unit, and determining whether the total turn-on time exceeds a pre-set value; (S4) if the total turn-on time exceeds the pre-set value and it has not been detected over a continuous third pre-set time that the oil volume of the compressor is insufficient, recycling oil back to an oil storage tank by controlling a switch unit and the oil volume adjusting unit.