Abstract: The optical characteristics of jet injecting aerodynamic window with big exit aperture have studied experimentally. The Strehl ratio,wavefront aberration and coefficients of Zernike polynomial of laser beam,passed through the aerodynamic window,were given up from the data,collected by HARTMANN diagnostic apparatus. From these optical characteristics it can be analyze,that the injection flow pressure and the structure of aerodynamic window influence on the passed beam quality.It was shown that the passed beam will be divergence,as the injection flow pressure becomes large. It is related to that the axial grads of air density distribution,caused by gas flow from circular nozzle,become large. And heterogeneous distribution of air bleed hole makes the wavefront tilt so that the passed laser beam will shift.