Full annulus steady and transient numerical simulations are performed on a lowspeed axialflow compressor isolatedrotor test rig and NASA Rotor 37. Two new boundary methods, i.e. nozzle outlet and throttle outlet, are adopted instead of the traditional outlet boundary condition. The rotor's operation point can be adjusted by changing the computation domain's outlet area and throttle coefficient individually. The simulation results show that compared with the traditional method, the two new methods can calculate the rotor flow field under all mass flow status, including the near stall status and after stall status. By adjusting the throttle coefficient, the "throttle outlet" model can capture the critical stall point accurately, and by so doing this can figure out the way how reversed flow region emerges and develops in the rotor passages. The research finds that the instability flow structure in the blade tip region，i.e. the local reverse flow regions' formation and expansion processes, plays an important role in the two compressor rotors' stall characteristics. The fullannulus transient numerical simulation of the lowspeed axialflow compressor isolatedrotor finds that once the rotor comes to the stall state, two stall regions arise in the blade tip. The two stall regions expand with the increase of rotor revolutions, and the relatively significant stall regions come into being at last.