A head-up display (HUD) is directly influenced by altitude and high temperature because these factors have a critical effect on the LEDs that are used as light sources. Thus, research on cooling systems according to altitude is required. Sunlight and other thermal factors can cause the temperatures in a vehicle to reach or exceed 90°C. This severe environmental condition has a substantial impact on an HUD regardless of the method of HUD operation. An altitude adaptive cooling system was designed in this study to suppress the decrease in HUD brightness by minimizing the impact of temperature variations on the light source, thereby maximizing LED brightness efficiency. In high altitude areas where air is rarefied, the air density is low and the cooling efficiency rapidly falls even if the FAN rotation speed is increased compared to the speeds used in low altitude areas. A method that adaptively controls the FAN rotation speed based on altitude was studied to consistently maintain the internal temperature of the HUD system in high-altitude conditions. To achieve this, an algorithm that judges the accurate altitude and, based on this altitude calculation, an altitude adaptive cooling system were studied in the hopes that this system would to prevent abnormal operation of the HUD cooling system when errors occur when operating the HUD at high altitude.