Abstract: The paper conducts the 3D simulation of microwave pulses propagating, reflecting and transmitting in a building, to analyze the distribution of the maximum value of electric field in time domain. For narrow-band modulated square pulses with different incident angles, the size of field enhancement region is in direct proportion to the size of region irradiated by microwaves directly through the windows and doors, and the size of windows exerts great influence upon the the size of field enhancement region. The field amplitude in the area behind windowsills reduces significantly in the propagation direction of microwave pulse. The pulse width has little influence upon the size of field enhancement region and the maximum value of electric field. For narrow-band modulated square pulses with zer