A printing head suitable for 3D forming of a large complex geologic model comprises a printing head mounting plate, a printing nozzle fast replacement mechanism, similar material feeding pipes, a similar material circulation blocking prevention mechanism and a similar material flushing and purification blocking prevention mechanism, wherein the printing nozzle fast replacement mechanism comprisesa printing nozzle fast replacement driving motor, a motor mounting rack, a pipeline through connection plate and a printing nozzle through connection plate; three printing nozzles are evenly distributed on the printing nozzle through connection plate, the nozzle diameters of the three printing nozzles are different, and the printing accuracy goes from high to low; the similar material circulationblocking prevention mechanism comprises a similar material circulation feeding pipe, a similar material circulation feedback pipe and a similar material circulation material pipe quick receiving mechanism; and the similar material flushing and purification blocking prevention mechanism comprises a water inlet pipe, a water outlet pipe and a water pipe quick receiving mechanism. According to the printing head, the printing accuracy can be quickly adjusted, and a similar material circulation blocking prevention function or a similar material flushing and purification blocking prevention functioncan be started to use according to the lengths of pause durations in the time of printing pause.