Abstract: The light spot distortion effect of femtosecond laser pulses propagating through an acousto-optical deflector (AOD) was analyzed. Because of wide spectrum bandwidth of the mode-locked laser, When the AOD works, the light spot of the 1st diffraction order will be distorted by significant angular dispersion, thus reduces the spatial resolution of the image. With femtosecond laser pass AOD working at different acoustic frequencies, The shape and size of light spots were recorded, demonstrated the spot distortion properties.