The utility model relates to an improved square box type heating furnace, particularly a heating device applied to oil fields. The utility model is composed of a furnace wall, and furnace pipes arranged in a furnace chamber, and a fire nozzle is arranged in a furnace mouth. The utility model is characterized in that the furnace pipes are fixed with protective plates. The utility model has the advantage that flames can be blocked to be prevented from directly heating the furnace pipes as part of the furnace pipes are provided with protective plates. Thus, the heating temperature of the furnace pipes of positions having concentrated flames can be obviously reduced, and the service life of the furnace pipes can be prolonged. Thus, the maintenance times and the maintenance load can be reduced, and the regular production of oil wells can be assured.