The invention discloses an on-spot mapping device for construction project costs. The device comprises a protective device, wherein a supporting device is arranged on the bottom surface of the protective device; through a fixing device, a mapping instrument can be conveniently fixed and disassembled by mapping personnel, so that the mapping instrument can be maintained; through a suspension device, the mapping personnel can quickly and accurately carry out centering operation, so that the mapping speed is increased, and thus the accuracy of mapping is further improved; through the cooperationof the protective device, a clamping device, the suspension device and a lifting device, the mapping instrument can pop out from the interior of the protective device and be engaged in the mapping work; through the cooperation of the clamping device and the lifting device, the mapping instrument can be retightened to the interior of the protective device by directly pressing a sealing plug after the mapping instrument is used by the mapping personnel, an operation process is simple and rapid, very convenient to implement, time-saving and labor-saving, the working efficiency is improved, the mapping speed is further increased, and the practicability of the on-spot mapping device for the construction project costs is improved.