In order to explore the artificial cultivation technology of Sargassum polycystum, raft culture of S. polycystum was conducted during March to June, 2015 in Haitou Town of Danzhou city, Hainan Province. The growth rhythm of S, polycystum was recorded, and the effects of different cultivation conditions including water depth and culture density on growth were compared. The results showed that the cultured S, polycystum grew very fast from late-March to late-May, the length increased markedly before middle-April, while the weight kept increasing at a relative stable rate until the end of May. The algae length and branch number were influenced significantly by water depth and culture density respectively, while the fresh weight was obviously influenced by both of the above factors (P<0.05). This study indicated that properly increasing the water depth and choosing rational density could effectively promote the growth of S. polycystum. To increase the yield, the water depth should be set at around 80 cm, and the densities would be better set at 10 cm.