The invention discloses a multi-split air-conditioning system, comprising an oil-gas separator, a compressor, a one-way valve, an oil-return capillary pipe, an oil balance electromagnetic valve, an oil balance stop valve and an oil balance pipe, wherein an oil-return opening of the oil-gas separator communicates with the compressor through the oil-return capillary pipe, the one-way valve and the oil balance electromagnetic valve in sequence; the oil balance stop valve communicates between the one-way valve and the oil balance electromagnetic valve through a three-way valve and the oil balance pipe; and the one-way valve is on along the direction from the oil-return capillary pipe to the oil balance electromagnetic valve. According to the multi-split air-conditioning system, the oil-return capillary pipe is disposed between the one-way valve and the oil-gas separator; as the oil-return capillary pipe has the effects of throttling and pressure reduction, pressure in the oil-gas separator can be reduced to be close to the pressure of the oil balance pipe, the amounts of a refrigerant and lubricating oil which enter the oil balance pipe are reduced, the risk of pipe explosion can be greatly reduced. An unloading valve is omitted in the multi-split air-conditioning system, the structure is simplified and the safety is improved. The invention also discloses a method, applied to the multi-split air-conditioning system, for preventing pipe explosion of the oil balance pipe.