This article focuses on the Namdaemum repair and the Seokguram restoration, which had begun in 1961, as an important repair conducted during the time of seeking the conservation principle of architectural heritage after liberation in Korea. Through the analysis of the principles described in the repair report issued after the two repairs, meeting records, and related expert announcements, it is shown that the principle of 'preservation of the historic state' had been established at Namdaemun repair and later have changed to the principle of 'restoration of the historic form' which means reconstruction in Seokguram restoration. By analyzing the minutes of the Cultural Heritage Committee's meeting on the repair of other cultural properties during this period, it is revealed that the key terms related to the preservation principle, 'historic form' and 'restoration', were given meaning as 'object' and 'method' of preservation, and then 'restoration of the historic form' has been gradually used as a conservation principle.