Concrete 3D printing nozzle and 3D printer

The concrete 3D printing spray head structurally comprises a mechanical arm, a printing mechanism, a movable rod, a rotating disc and a base, the printing mechanism is fixedly embedded in the lower end of the mechanical arm, the mechanical arm is installed at the upper end of the movable rod, the movable rod is fixedly embedded in the rotating disc, and the rotating disc is installed at the upper end of the base; the sliding ring pushes the outer side of the spray head pipe, then the guide plate obliquely rotates with the rotating rod as the center, the inclination angle of the spray head pipe is changed, the diameter of the spray head pipe is adjusted while printing is conducted, and the situation that due to replacement, pause and incomplete connection are caused is prevented; under the elastic force of the arc-shaped plates, the outer sides of the triangular plates and the deformation plates generate elastic blocking on the concrete, the elastic blocking buffers the impact pressure of the concrete, and whe