A heating furnace for testing middle and long span structures including a modular partition structure to adjust an inner volume of the heating furnace, effectively performing a load-coupled heating test of full scale members such as a beam, a short column, a slab, a conjunction frame, and a deck plate. The heating furnace for testing middle and long span structures includes a partition unit formed of a refractory material and partitioning a heating space in a main body to block transfer of heat generated from one space to the other space. A test sample is installed in the heating space of the main body partitioned by the partition unit according to a size of the test sample, and then, heat and a compression force are applied to the test sample to perform a fireproof performance test. The fireproof performance test of structure members having various lengths of 4 m, 6 m and 10 m can be performed, and consumption of various utilities consumed during the test can be optimized. In addition, since the heating furnace can perform an actual material test of full scale structures such as continuous span beams and long span beams, deck plates, or bridge trusses of civil structures, deck plates for ships, and so on, target fireproof performance estimation of various shape conditions can be performed to increase applicability of the test.