A multi-split air-conditioner and an outdoor unit system thereof are provided. The outdoor unit system includes: a compressor (1) having a gas outlet (a) and a gas inlet (b); an outdoor heat exchanger (2) having an inlet (c) and an outlet (d); a switching assembly (3) having first to sixth ports, wherein the first port (e) is connected with the gas outlet (a) of the compressor (1), the second port (f) is connected with the gas inlet (b) of the compressor (1), the third port (g) is connected with the inlet (c) of the outdoor heat exchanger (2), the fourth port (h) is connected with the outlet (d) of the outdoor heat exchanger (2), the fifth port (i) is connected with an inlet pipe (4) and the sixth port (j) is connected with an outlet pipe (5).