A ranging method, comprising: a) receiving, by a ranging device, ranging data obtained by a plurality of laser radars of a laser radar system, wherein the ranging data comprises distances between the laser radars and obstacles in measurement ranges of the laser radars, and the plurality of laser radars comprises a target laser radar installed on a target unmanned driving device, said ranging method being characterized in that it further comprises the steps of: b) establishing, by the ranging device, a three-dimensional coordinate model according to the ranging data, wherein the three-dimensional coordinate model comprises the coordinates of each laser radar and the coordinates of an obstacle measured by each laser radar; wherein the establishing, by the ranging device, a three-dimensional coordinate model according to the ranging data comprises: establishing a three-dimensional coordinate system with the location of the target unmanned driving device as origin, according to the target ranging data obtained by the target laser radar installed on the target unmanned driving device; and according to other ranging data different from the target ranging data, determining the coordinates of another laser radar among the plurality of laser radars except the target laser radar and the coordinates of each obstacle in a measurement range of the other laser radar, to obtain the three-dimensional coordinate model; c) determining, by the ranging device, the distance between the target unmanned driving device and each obstacle according to the three-dimensional coordinate model; and d) sending the distance between the target unmanned driving device and each obstacle to the target unmanned driving device, so that the target unmanned driving device performs ranging calibration according to the distance on a visual image algorithm used for ranging. a) receiving, by a ranging device, ranging data obtained by a plurality of laser radars of a laser radar system, wherein the ranging data comprises distances between the laser radars and obstacles in measurement ranges of the laser radars, and the plurality of laser radars comprises a target laser radar installed on a target unmanned driving device, b) establishing, by the ranging device, a three-dimensional coordinate model according to the ranging data, wherein the three-dimensional coordinate model comprises the coordinates of each laser radar and the coordinates of an obstacle measured by each laser radar; wherein the establishing, by the ranging device, a three-dimensional coordinate model according to the ranging data comprises: establishing a three-dimensional coordinate system with the location of the target unmanned driving device as origin, according to the target ranging data obtained by the target laser radar installed on the target unmanned driving device; and according to other ranging data different from the target ranging data, determining the coordinates of another laser radar among the plurality of laser radars except the target laser radar and the coordinates of each obstacle in a measurement range of the other laser radar, to obtain the three-dimensional coordinate model; establishing a three-dimensional coordinate system with the location of the target unmanned driving device as origin, according to the target ranging data obtained by the target laser radar installed on the target unmanned driving device; and according to other ranging data different from the target ranging data, determining the coordinates of another laser radar among the plurality of laser radars except the target laser radar and the coordinates of each obstacle in a measurement range of the other laser radar, to obtain the three-dimensional coordinate model; c) determining, by the ranging device, the distance between the target unmanned driving device and each obstacle according to the three-dimensional coordinate model; and d) sending the distance between the target unmanned driving device and each obstacle to the target unmanned driving device, so that the target unmanned driving device performs ranging calibration according to the distance on a visual image algorithm used for ranging.