The mountainous roads are rugged and complex, so that the driver can not make accurate judgments on dangerous road conditions. In addition, most heavy vehicles have characteristics of large weight and high center of gravity. The two factors above have caused most of the car accidents in mountain areas. A research shows that 90% of car accidents can be avoided if drivers can respond within 2-3 seconds before the accidents happen.This paper proposes a speed warning scheme for heavy-duty vehicle over the horizon in mountainous area, which can give the drivers enough time to respond to the danger. In the early warning aspect, this system combines the front road information, the vehicle characteristics and real-time information obtained from the vehicle, calculates and forecasts the danger that may happen over the horizon ahead of time, and prompts the driver to control the vehicle speed. Compared to the road standard speed limit, the combination of the road information and characteristics of heavy vehicle itself can provide a more accurate and more useful safety warning speed limit. Results of hardware-in-the-loop simulation show that this system can effectively reduce the brake temperature in the downhill, prevent rollover in the curve, and improve the heavy vehicle driving safety.