A microchannel heat exchanger (100) with improvement of dirt-resisting and anti-blocking is disclosed. The microchannel heat exchanger (100) includes at least two heat exchanger units (101, 102) vertically arranged in parallel with the top one being a first heat exchanger unit (101) and the bottom one being a second heat exchanger unit (102). Every heat exchanger unit (101, 102) includes: a first heat tube (103) and a second heat tube (104) oppositely arranged in the horizontal direction; and multiple flat tubes (105) extending between the first and second heat tubes (103, 104) and having both ends communicated with the first and second heat tubes (103, 104). The microchannel heat exchanger (100) also includes multiple fins (109) each arranged between and in contact with the neighboring flat tubes (105) of the same heat exchanger unit and extending from the first heat exchanger unit (101) to the second heat exchanger unit (102). The microchannel heat exchanger (100) overcomes the disadvantage of becoming dirty and blocking and has excellent heat dissipation effect.