Based on comprehensive analysis of vehicle infrared assisted driving safety braking process, infrared static detection model and dynamic detection model, the model of visual range for assistant driving safety was established. The relationship between maximum safe speed, road condition, infrared detection performance was analyzed. It is found that it is mainly related to sliding adhesion coefficient and detection distance. Through the correction calculation of infrared detection distance, the maximum safe speed at night was simulated. The results show that it is mainly affected by the temperature difference between target and background. Emphasis is laid on foggy and rainy weather for example analysis. The results show that foggy weather mainly affects the detection distance, especially when the visibility is less than 1 km, and the maximum safe speed need be controlled at 21-25 km/h when the visibility is 5 km. Rainy weather will affect the sliding adhesion coefficient and detection distance. The maximum safe speed control under infrared recognition is the main method for assistant driving. When rainfall intensity is 50 mm/h, the maximum safe speed need be controlled at 12-14 km/h.