Aiming at the problem that the changes of night brightness of a certain type of LCD is not uniform, which affects the use’s visual measurement of information in the night environment, the problem is analyzed in combination with the design scheme, and formulates the external positive measures. Based on the actual test value of PWM output of each gear and level, the parameters are adjusted to ensure that the output of each level is consistent with the brightness requirements. Through this solution, when the luminance data is 9, the measured luminance is 0.787 5 cd/m2, which meets the requirements of the index(0.726～0.921 cd/m2). The measured value in luminance between 0 and 9 is improved from 1.124 cd/m2 to 0.712 55 cd/m2, and the measured change in luminance between 9 and 18 is improved from 0.246 cd/m2 to 0.772 5 cd/m2. The variation of the measured value of true degree between each gear is similar and uniform, which improves the display effect and meets the user’s requirement.