4 royal palaces are currently remained from capital city (Seoul) of 'Cho-Sun(朝鮮)' period. In these palaces, 'Main hall of Royal Palace(正殿)' is the center of the Royal Palaces. The 'Main hall of Royal Palace' of the Royal Palace was the best building of that time. Therefore there were many studies about the 'Main hall of Royal Palace'. But these studies were individual studies of these 'Main hall of Royal Palace'. Therefore, this study is to analyze and compare 4 'Main hall of Royal Palace' of the Royal palaces. It is to study the proportion regarding the Diameter of the pillar, the Height, the pillar and pillar Interval's Distance, and the arrangement of 'Kong-Po(bracket sets)'. With these studies, it is to prove that the 'Main hall of Royal Palace' is the building which high construction technique of this time is expressed. Result of this study is as followings; First, the proportion of pillar height(H) to its diameter(D) average from H=8.0 to 8.5D. Only the Myeong-Jeong-Jeon omitted the 'Go-Ju(高柱)' in the 'Toi-Kan (退間)' to place Ea-Jwa(御座). Second, Second, the proportion of diameter of the pillar of 'Eoi-Bu-Pyeong-Ju(外部平柱)' and 'Nae-Jin-Go-Ju(內陣高柱)' average D1(Diameter of 'Eoi-Bu-Pyeong-Ju') =0.91D2 (Diameter of 'Nae-Jin-Go-Ju'). In regards to the height, the single floor 'Main hall of Royal Palace' and double floor 'Main hall of Royal Palace' seems to be different. The height proportion of the double floor 'Main hall of royal palace' is H1(Height of 'Eoi-Bu-Pyeong-Ju')=0.34H2(Height of 'Nae-Jin-Go-Ju') and single floor 'Main hall of Royal Palace' has a proportion of H1=0.62H2. Third, in Geun-Jeong-Jeon, with the proportion of height and diameter of the pillar, interval's distance between pillars and diameter, the pillar interval distance and height, of 'Ea-kan(御間)' from the 'Toi-Kan' is different from 'Main hall of Royal Palace'. This is because the structure of 'Toi-Kan' of Geun-Jeong-Jeon is not stable. In order to reinforce this, 'Gui-Go-Ju(隅高柱)' of the Geun-Jeong-Jeon jut out $4{\sim}7%$ more compared to In-Jeong-Jeon. Fourth, when comparing double floor 'Main hall of royal palace' of Geun-Jeong-Jeon and In-Jeong-Jeon, based on distance of 'Eoi-Bu-Pyeong-Ju' and 'Nae-Jin-Go-Ju' of lower level, the 'Sang-Bu-Pyeong-Ju(上部平柱)' of Geun-Jeong-Jeon jut out $4{\sim}7%$ more compared to the In-Jeong-Jeon and also It becomes thicker. Fifth, the arrangement of 'Kong-Po' on the front row of 'Gan(間)' had to do with the change of side 'Gan'. Even though the Geun-Jeong-Jeon and the In-Jeong-Jeon were double floors, the arrangement of the 'Kong-Po' is different because the number of side bay is different.