Characteristics　of　flow　field　in　Laval　micronozzles　with　34　μm　throat-width　were　studied　numerically　by　using　continuum　and　direct　simulation　Monte　Carlo　(DSMC)　method.　Three　types　of　micronozzles　with　different　throat　shapes　were　designed,　such　as:　sharp-corner,　smooth-corner　and　flat-corner.　Based　on　the　geometric　structure　design,　effects　of　throat　shape　and　expansion　ratio　on　flow　field　and　propulsion　performance　were　analyzed,　respectively.　It　is　discovered　from　the　results　that,　the　comprehensive　propulsion　performance　of　the　micronozzle　with　smooth-corner　throat　is　the　best,　while　the　micronozzle　with　flat-corner　throat　has　much　better　specific　impulse　efficiency.　When　the　expansion　ratio　becomes　larger,　both　thrust　and　specific　impulse　will　increase.