Laser-controlled land leveling system can obviously improve the planeness of the field and enhance the efficiency of irrigation. The 3D topographic information was needed for project design and evaluation of laser land leveling. In order to obtain the topographic information efficiently, an onboard field 3D topography surveying system was developed. The surveying system consisted of a measuring laser receiver, a GPS receiver, a controller and a hydraulic system. Besides topographic measurement, the system could also achieve laser land leveling. The measuring laser receiver was used to obtain the elevation and the GPS receiver was employed to obtain the longitude and latitude data. The data was fused in the controller to get the 3D topographic information. Field experiments were carried out in different speed and compared with the data from the fixed-point surveying method. The result showed the surveying system had a good consistency with the fixed-point surveying method in slower speed.