The invention provides an air conditioning system, a controlling method and air conditioner. The air conditioning system comprises a compressor, a condenser and an evaporator, further comprise an oiltank, wherein the oil tank communicates with a gas suction port of the compressor through a balance pipe, the air conditioning system further comprises a primary injection device, the primary injection device comprises a first injector, the first high-pressure injection end of the first injector communicates with the condenser, the first low-pressure injection end communicates with the evaporator,and the first outlet end of the first injector communicates with the oil tank. According to the air conditioning system, the controlling method and the air conditioner, a scheme that oil is directlyinjected to the gas suction port of the compressor is abolished, and the oil is prevented from being directly injected to the gas suction port of the compressor to be taken away by a gas flow, so thatthe condition that the compressor is caused to lack the oil is avoided, normal oil return when the compressor sucks is guaranteed, a secondary injection pipeline is removed, a primary injection pipeline is directly connected with the oil tank, the combination of oil return injection and oil cooling assistance is adopted, the times of oil soaking of the balance pipe can be reduced, and the stressstrain of the long-segment pipeline can be reduced as well.