The invention discloses a low-temperature high-pressure resistant electric heater in the field of electric heating devices and a manufacturing method thereof. The manufacturing method includes the following steps: preparing the corresponding length of an electric heat pipe, a resistance wire, a conductive lead rod and a protecting pipe, placing the protecting tube vertically, and stretching the resistance wire into the protecting tube; vertically placing the electric heating tube, putting the protecting tube into the electric heating tube, filling the magnesium oxide powder into the electric heating tube, keeping the protecting tube in the centering, removing the protecting tube out of the electric heating tube, carrying out pressure withstand test on the electric heating tube, reducing the diameter of the electric heating tube and sizing the axial length; the outer periphery of the electric heating tube is wound and provided with a heat radiating fin bending processing and forming; the tube mouth of the electric heating tube is sealed by silica gel, and an insulating terminal and a conductive rod fastener are arranged at the sealing end of the electric heating tube. The electric heater is processed by the method. According to the invention, the side of the wall of the electric heating tube can be prevented from being broken down under the high-pressure impact, the heat supplyis prevented from being interrupted, and the personal safety hazard is avoided.