A micro-multi channel heat exchanger includes a lower header having a hollow for receiving refrigerant and an upper header opposite to the lower header. A plurality of tubes are arranged in a length direction of the upper and lower headers at fixed intervals, each having opposite ends fixed to the upper header and the lower header. A plurality of channels are formed in the tubes and elongated to be in communication with the hollows of the two headers. Each channel has an area of a section, parallel to a length direction of the two headers, reducing at a fixed ratio as the channels go from an air inlet side to an air outlet side. A plurality of fins are located between the tubes for heat exchange with the air.