The invention discloses a combined type direct-heating resistance furnace. The combined type direct-heating resistance furnace is composed of a heating unit set and a heat exchange system, wherein the heating unit set is composed of a plurality of resistance heating units, and each resistance heating unit is composed of a unit shell, a resistance heater assembly, an insulating heat-conducting medium, an insulating sleeve, a medium outlet, a medium inlet and an insulating layer; each resistance heater assembly is composed of a metal wire and a structural component used for supporting and fixing the conducting and heating metal wire; the heat exchange system is composed of a plurality of sets of medium circulating pumps, a medium heat exchanger and a heat circulating pipeline. According to the combined type direct-heating resistance furnace, the resistance heating units are interchangeable, and the working voltage and heating power of the combined type direct-heating resistance furnace can be changed by changing the mode of wire connection between the resistance heating units; due to the fact that the resistance heater assemblies are immersed in the insulating heat-conducting medium, the insulation grade of the resistance heater assemblies is improved, the sizes of the resistance heating units are reduced, and equipment instillation area is reduced; the combined type direct-heating resistance furnace can work reliably by manufacturing the unit shells with normal-pressure vessels.