According to the characteristics of supersonic and subsonic flow, the Prandtl-Meyer expansion wave theory, and the Mach number after expansion waves based on the back pressure and static pressure, the bleed mass flow rate was obtained, the conditions for the occurrence of choking were derived, and a two-dimensional supersonic bleed model was established. According to the impulse theorem, based on the assumption that the state change of gas from the main flow area to the bleed chamber was due to the impulse effect of the pressure difference, a subsonic bleed model was established and the mechanism of subsonic bleed chocking was revealed. CFD(computational fluid dynamics) verification shows that the deviation of the subsonic bleed impulse model is considerable, so the subsonic bleed flow was described by a numerical fitting model. This study provides a reference for three-dimensional bleed research.