Aiming at the problem of overbrightness of the target simulator background for LED backlight panel illumination, a 5° aperture angle-matched collimated illumination method for the target simulator is proposed based on the study of the dark-state leakage of the LCD display device and the scattered stray light of the system. After simulation analysis the method can make the display contrast increase by 3.1 times and solve the problem of dark targets being drowned by the background bright light, which exists in the LED illumination target simulator. It is experimentally verified that the target simulator using the aperture angle-matched collimated illumination method shows a 2.8 times improvement in SNR and effectively reduces the energy of the dark-state background.