A kind of automatic and adjustable illumination system was designed to improve the poor precision in the measurement of strong ocular aberration of human by a narrow parallel beam illumination.By adding a position adjustable collimation lens in the light path,the diopter of illumination light source could be precisely controlled by adjusting the lens,and the position of collimation lens could be exactly and rapidly scanned and located by a motorized stage. Moreover,the aberrations of a model eye are measured by the narrow parallel beam illumination system and by the adjustable illumination system in this experiment respectively. The obtained results show that the Peak Signals to Noise Ratio(PSNR) of the image got by the sensor in the automatic and adjustable illumination system are improved from 5.72 dB to 19.89 dB,and the average defocuses of a -5 m-1 model eye is changed from -(4.285±0.208) m-1 to -(5.041±0.157) m-1 as compared with that of the narrow parallel beam illumination. These data show that the PSNR of the image for Hartmann-Shack sensor has been obviously improved by the automatic and adjustable illumination system,which makes the measurement result more accurate.