The vehicle LIDAR has been widely used in the fields of three-dimensional city modeling, terrain mapping, the agroforestry ecosystem, military detection, and unmanned driving for its advantages of high resolution, strong anti-interference ability, small volume, and light weight. The measurement accuracy of vehicle LIDARs is influenced by the internal heat source of the system and the external ambient temperature to a great extent. A compact vehicle LIDAR system is designed and analyzed. Combined with the distribution characteristics of the internal heat source of the LIDAR system, the temperature distribution and thermal deformation in the LIDAR system under different external temperatures are analyzed. On this basis, the laser path deviation of the LIDAR system caused by thermal deformation is also analyzed and compared. Finally, when the ambient temperature changes from −10  °  C to 50°C, the deviation of the laser output angle is within ±0.1 mrad by optimizing the design, which meets the requirements of the measurement accuracy of the vehicle’s LIDAR.