Experiments　of　the　pressure　drop　instability　of　flow　boiling　with　FC-72　in　8　parallel　rectangle　microchannels　with　a　hydraulic　diameter　of　88　pm　were　conducted　in　this　study.　The　mass　flux　ranges　from　578.2　to　2310.9　kg/m(2)　s,　the　heat　flux　ranges　from　0　to　1200　kW/m(2)　and　the　measured　pressure　drop　ranges　from　13　to　275　kPa.　The　compressive　volume　in　a　nitrogen　vessel　before　the　test　microchannels　is　set　as　0,　5　and　15　ml　in　the　experiments.　The　experimental　results　of　heat　transfer,　pressure　drop　and　the　corresponding　flow　patterns　are　presented　and　analyzed.　Furthermore,　the　critical　vapour　qualities　at　the　onset　of　the　flow　boiling　instability　(OFBI)　are　predicted　by　a　theoretical　model　considering　the　local　pressure　and　the　frictional　pressure　resistances.　The　calculated　and　experimental　results　indicate　that　the　instable　zones　in　a　flow　boiling　stability　map　expand　with　increasing　the　compressive　volume　and　decreasing　the　two　types　of　resistances.　The　critical　vapour　quality　at　OFBI　changes　from　0.65　to　1　when　the　local　pressure　resistance　combination　coefficient　is　increased　to　7.33　x　10(-3)　or　the　frictional　pressure　resistance　combination　coefficient　is　increased　to　0.532.　The　physical　mechanisms　behind　the　phenomena　are　discussed　according　to　the　experimental　results.