The article explains that the district of Tai-hu Lake hadn’t undergone transgression in the past six thousand years and it was not formed from lagoon environment.1. By the analysis of trace-element in the peat bed of 6000 yr Bp., it is considered that the farthest boundary of the transgression in Tai-hu Lake district in the Holocene, is on the east side of the shell ridge formed 5680?80 years ago.2. The deposits of the middle Holocene dated by 14C show that they are neither marine-deposits nor lagoon deposits, but continental ones. Their depth is generally 3 or 5 meters under earth surface.3. The discovery of ruins and relics of the past seven thousand years proves that Tai-hu Lake district was already a land by that time and has never experienced transgression. The ancient culture layer 11 m thick is practically a continuous layer for seven thousand years. It strongly proves the Tai-hu Lake district had not experienced any transgression since the last seven thousand years.The auther concludes that Tai-hu Lake wasn ’t a lagoon, but a tectonic lake, formed by block of river courses by neotectonic movement.