The camera DMS and OMS in the car cabin identify the mental state, vital characteristics, and body expression of the occupants. In order to ensure the success rate of the algorithm recognition, there are certain requirements for the brightness of the face or body in the image. In view of the feature of near infrared imaging requiring active light source, a technical scheme of near infrared light supplement for the camera in the car cabin is proposed. A calculation model is established based on the theories of spatial flux distribution of infrared radiation source, near infrared characteristics of human skin, refractive and reflective law of geometric optics, photoelectric conversion ability of Sensor, etc. The relationship formula between the power of the fill light LED and the face brightness DN value in the image is derived. In the data model, the formula is used to calculate the luminance DN value of the face captured in the image after the 5.2 W near infrared supplementary light LED is used to fill the light. At the same time, a verification system is set up for the camera inside the cabin. Through the analysis of the brightness DN value of the image data taken by the test vehicle after the actual light filling, and the comparison with the theoretical calculation results, the error between the experimental results and the calculated results is less than ±5%, which meets the algorithm requirements, and verifies the feasibility of the technical scheme of near infrared light filling for the camera inside the cabin.