Since the Tang Dynasty, there was a climax of building Giant Buddhas in Sichuan area, and ten Giant Buddhas over 10 meters appeared successively. This paper investigates the construction history of Giant Buddha in Tongnan and compares it with the Giant Stone Buddha at Leshan Mountain and by reference to it. It points out that the shadow of the Giant Stone Buddha at Leshan Mountain can be seen the Giant Buddha in Tongnan, which shows that the relationship between them is very close. Feng Hui of Song Dynasty said that the Giant Stone Buddha at Leshan Mountain ranked first at that time and Giant Buddha in Tongnan ranked second, which is based on the fact, and they are all the same Maitreya Buddha of the class.