The invention relates to an air conditioner and a control method thereof. The air conditioner comprises an outdoor heat exchanger, a four-way valve, a compressor, an indoor heat exchanger and a throttle mechanism, wherein the throttle mechanism is connected between the outdoor heat exchanger and the indoor heat exchanger in series. The invention is characterized in that more than two different-flow gears which can be shifted according to the circulation mode and the operating frequency of the compressor are arranged in the throttle mechanism. The throttle mechanism comprises a three-way valve. The first interface of the three-way valve is communicated with one end of the outdoor heat exchanger, the second interface of the three-way valve is communicated with one end of a first capillary and the third interface of the three-way valve is communicated with one end of a second capillary. The other end of the first capillary is connected with the other end of the second capillary in parallel and then is communicated with one end of the indoor heat exchanger. The flow of the first capillary is less than the flow of the second capillary. The invention has the advantages that the operation is flexible, the manufacturing cost is low, the application scope is wide, the energy efficiency of the air conditioner can be effectively improved, and the maximum operating ability and the low-temperature refrigerating ability of the air conditioner can be also improved.