The invention discloses a heat exchanger with a micro-channel, parallel-flow and all-aluminum flat pipe welding structure. The heat exchange part of the heat exchanger is formed by arranging flat pipes consisting of aluminum extruded thin-walled sections in parallel. Compared with the prior art, the heat exchanger with the micro-channel, parallel-flow and all-aluminum flat pipe welding structure has the advantages that: 1, the heat exchange efficiency of a refrigerant and the inner walls of the flat pipes is improved by 40 percent, and the flow resistance of the refrigerant in collecting pipes of the heat exchanger is reduced by 40 percent; 2, the heat exchange efficiency of fins on an air side is improved by 40 percent, and the wind resistance of the heat exchanger on the air side is reduced by 40 percent; 3, the heat exchange performance of the whole heat exchanger is improved by 40 percent; 4, compared with the prior art, the heat exchanger consumes 40 percent less refrigerant; and5, compared with the conventional copper-aluminum structure, the all-aluminum structure endows the heat exchanger with longer service life because of no copper-aluminum potential differences. The heat exchanger adopting the flat pipes has the characteristics of capability of bearing the conventional limitation of high-pressure resistance value of the refrigerant, compact product structure, light unit weight, short process flow, high manufacturing reliability and relatively lower cost. The invention also discloses the application of the heat exchanger.