The invention provides a dead-reckoning navigation positioning method for acquiring the longitude and the latitude of an automobile by using a speedometer. The dead-reckoning navigation positioning method comprises the following steps: (1) differing running distance acquired by the speedometer so as to acquire the running speed and the orientation angle of the automobile; (2) reckoning the longitude and the latitude of the automobile according to the running speed and the orientation angle; (3) outputting the running speed, the orientation angle, the longitude and the latitude. According to the dead-reckoning navigation positioning method for acquiring the longitude and the latitude of the automobile by using the speedometer, only the automobile-mounted speedometer is adopted as a data source for acquiring the longitude and the latitude of the automobile, and with the combination of the present running speed and the orientation angle which are used as the output of a dead-reckoning system and not only a coordinate of a rectangular plane coordinate system, a dead-reckoning navigation positioning system which can directly provide the longitude and the latitude of the automobile is achieved; inertia devices such as a gyroscope and an accelerometer are not needed, so that the achieved dead-reckoning navigation positioning system which can directly provide the longitude and the latitude of the automobile is relatively low in cost. The invention further provides the dead-reckoning navigation positioning system.