Abstract: 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.