A discharge heat preserving method and device for a 3D printer are disclosed. A hot airflow is blown to a discharge outlet (111) of a nozzle device (110) mounted on the 3D printer to form a heat preserving area at the discharge outlet (111) of the nozzle device (110), a material discharged from the discharge outlet (111) of the nozzle device (110) stays for 2-10s in the heat preserving area and the hot airflow is blown to the discharge outlet (111) of the nozzle device (110) from a lateral direction of the nozzle device (110). Since the heat preserving area is formed at the discharge outlet (111) of the nozzle device (110), the material discharged from the discharge outlet (111) of the nozzle device (110) stays in the heat preserving area and the material is heated in the heat preserving area, the temperature of the material gradually decreases and the damage situations such as that the edge of the material is warped up and the material is broken after the material is solidified because the temperature of the material rapidly decreases are avoided. Utilizing the discharge heat preserving method and device can save energy and reduce the production difficulty caused by heating of the entire chamber to high temperature.