In this study, the firing method of the excavated large pottery jar are inferred, by observing the firing trace which appeared in the experiment in which long necked pot firing is implemented, and the traces which appear in the pots excavated from various remains, in comparison. In this experiment of long necked pot firing, a pot coffin for experiment object, was manufactured through divided molding method, in an open-air cover typed pot firing kiln which is covered with mud, taking the pots for coffin exclusive use from Yungsan River basin as the prototype model. In the analysis of firing trace in the experiment, in case of sealed pot firing, the pots which are baked into soft substance and hard substance, are mostly the result of firing for which the pot is vertically placed in the kiln. In this case, the appearance that the bottom part of the pot is transformed into soft substance, or that the dark spot which is intensified on the center part of the bottom remains, are shown, or the firing trace according to supporting bottom stone or the bottom separating material like sand in the kiln, remains. In cover type open air firing, dark spots are identified, in some part of the lower section of the body region of the pot, and also in some part of the bottom, in case that the pot is laid in tilted placement mode in kiln for firing, and the dark spots are identified even in mouth region and in the lower section of the body region, in case that the pot is laid in lateral placement mode. It is also found that the dark spots are formed even in the other parts except the bottom part and inside part of the pot according to being cover type open air firing, and the firing trace according to the collapsed wall of kiln, remains. Finally, viewing through wide observation, it is grasped that the firing trace is related to the major usage of large pottery jar according to respective regions. It seems, unlike other regions, particularly in the region of the Yungsan river basin, though sometimes exclusive kiln is manufactured and used for firing pots, as the scale of the large pottery jar had been enlarged radically according that the large pottery jar are used as exclusive use for coffin, mostly, the sealed open air firing method is used for manufacturing large pottery jar. The large pottery jar from Jeju region are grasped to have similar appearance with that of Japan in Yayoi age, in firing method, which might be a good ground for inferring the existence of cultural interaction between the two regions.