In order to solve the problem of unevenness in sensitivity distribution of 10 m×10 m large target area detection in indoors, the sensitivity distribution of the lens light-screen detection sensor was studied. According to the theory of lens photometry, the main factors influencing the sensitivity of light-screen detection were analyzed. The mathematical model of detection sensitivity was established, and the change trend of the amplitude of the projectile signal in different positions of the light-screen was obtained. Finally, the sensitivity correction scheme was proposed, and the evenly sensitivity distribution of the detection screen was realized by changing the luminous brightness of the light source at different positions. Using the air gun to verify the modified detection light-screen shows that the sensitivity to meet the evenly requirements of large target area sensitivity.