This paper is about time synchronization algorithms for Orthogonal Frequency Division Multiplexing (OFDM) system based on the features of underwater acoustic (UWA) channel. The three time synchronization algorithms are analyzed at the first place. Then on the basis of computer simulation, the performance of the three algorithms are compared and tested in the actual lab pool. Latter experimental results shows LFM chirp signals as synchronization symbol are more suitable for OFDM underwater communication system.