Flow　boiling　in　multi　micro-channel　evaporators　is　a　promising　approach　to　cooling　high　heat　flux　in　many　devices.　Understanding　of　the　fundamentals　of　flow　boiling　in　multi　microchannel　evaporators　is　urgently　needed.　This　paper　presents　a　critical　review　on　the　research　of　flow　boiling　phenomena　in　microchannels.　First,　classifications　of　macro-　and　micro-channels　are　briefed.　Then,　studies　on　flow　boiling　in　multi　microchannels　with　plain　surface　are　analyzed.　Next,　studies　of　flow　boiling　in　multi　microchannels　with　various　enhanced　technologies　are　analyzed.　Finally,　heat　transfer　mechanisms　and　development　of　prediction　methods　are　discussed.　According　to　the　critical　review　and　analysis　of　the　current　research　on　the　fundamental　issues　and　challenges　of　flow　boiling　in　micro-channels,　future　research　needs　have　been　identified　and　recommended.　In　general,　systematic,　and　accurate　experimental　data　of　flow　boiling　in　micro-channels　are　needed　by　using　advanced　measurement　technologies.　In　particular,　optimal　design　of　microchannel　evaporators　with　plain　surface　and　enhanced　structures　is　lacking　and　should　be　investigated.　The　physical　mechanisms　of　flow　boiling　should　be　further　investigated　based　on　the　corresponding　flow　patterns.　Furthermore,　mechanistic　prediction　methods　should　be　developed.　Furthermore,　systematic　experimental,　analytical　and　modeling　studies　on　transient　flow　boiling　phenomena　in　micro-channels　should　be　conducted　to　understand　the　physical　mechanisms　and　develop　the　theoretical　models.