The invention relates to a high-precision 3D (three-dimensional) printer with printing smoothness by double-nozzle technology. The high-precision 3D printer comprises a lifting measurement mechanism, a printing platform, a material disk, a wire feeding pipe, a lifting plate, a printing mechanism and two lifting units. The printing mechanism comprises a lifting rod, a second motor, a second driving shaft, a connecting block, a dredging mechanism and two nozzles, and the lifting measurement mechanism comprises a pull wire, a rotating disk, a driving gear, a driven gear, a roller, a key-phase cursor, a key-phase sensor and a supporting rod. When the high-precision 3D printer with printing smoothness by the double-nozzle technology is blocked, the second motor drives the connecting block to switch the nozzles, a pin is inserted into one blocked nozzle to dredge the blocked nozzle by the dredging mechanism, and smooth printing is ensured when the nozzles are switched again. Besides, when the lifting units run every time, the height of the printing mechanism can be increased by one layer by the aid of the lifting measurement mechanism, so that distances among layers of a printed sample can be equal, and high-precision printing is realized.