The invention discloses a self-service printing head of a 3D printer. The printing head comprises a nozzle assembly and a platform assembly; a bottom plate, a tray and a mechanical limiting mechanismare arranged on the platform assembly, wherein the bottom plate is arranged at the position, close to the lower edge and in the middle of the platform assembly, the tray is arranged on the bottom plate and is clamped on the platform assembly, the mechanical limiting mechanism is arranged at the edge of the bottom plate and is in contact with the tray; the nozzle assembly is arranged right above the tray, and comprises a nozzle outer cover, a nozzle mechanism, a piston mechanism and a residual material detection mechanism, wherein the nozzle mechanism is connected with the piston mechanism, thenozzle mechanism and the piston mechanism are arranged on the nozzle outer cover, the residual material detection mechanism is arranged on the piston mechanism, and the mechanical limiting mechanismis connected with the piston mechanism. The printing head has the beneficial effects that manual operation on the printer does not need to be carried out in real time, a printed product can be obtained in a self-service mode, the normal use of the printer is not influenced, so that the working efficiency of the printer is improved; and the printing speed and the printing stability are improved, and the printer is suitable for printing various food.