A combustion cylinder construction for an oil space heater is disclosed which is constructed to dispose a uniform air flow forming mechanism between an outermost heat-permeable cylinder and an outer cylindrical member of a double combustion cylinder, thereby not only to keep the double combustion cylinder in a red-heated state, but also to carry out the formation of a uniform and stable white-yellow flame and to complete combustion at a flame spreading means. There is also disclosed a combustion cylinder construction which further includes a heat ray reflecting means to render the temperature profiles through the heat-permeable cylinder as uniform as possible, resulting in an oil space heater having a long service life.