The invention discloses a navigation data based long-downhill path early warning method and system for a vehicle. The method comprises the following steps: carrying out gridding division on navigationmap data, and numbering grids; extracting early warning service point data in the navigation map data, wherein early warning service points comprise long-downhill path early warning points and risk avoiding service points; acquiring dotted early warning data including all early warning service point data in the grids; judging whether long-downhill path early warning points exist in one grid in which the vehicle is currently located and surrounding grids or not according to the dotted early warning data; performing safety early warning if the long-downhill path early warning points exist, andindicating the risk avoiding service points around the vehicle at the same time. Therefore, searching speed can be effectively accelerated, and under a condition of the same consumption of hardware memory resources, a distance range can be searched even further; the surrounding early warning service points can be provided for a driver, so that the driver can conveniently get ready for long-downhill path sections in advance.