Experiments in this study on the effect of water temperature upon the development of pelagospheric larvae of peanut worm Sipunculus nudus were conducted over larvae from swimming period to setting stage, in which, parents worms used for larvaeproducing were collected from native sea waters, and larvae were obtained by manmade induction to spawning and hatching. The results showed that the development durations of larval S.nudus from swimming to setting stage were closely related to the change in water temperature with a relationship in response to Logistic curve, indicating an optimum temperature range of 27.5-32.0 ℃ for the development of the larvae at swimming stage, a critical range of 27.5-28.0 ℃ and an optimum temperature of 30.0-34.0 ℃ for the larvae at metamorphosing, with the evidence that at 30 ℃ or above larvae at metamorphosing could arrive at obviously higher rates of both metamorphosis and postmetamorphosed survival, and the survival rate of postmetamorphosis being above 20%. Discussions were also given in this study to explore the possibility that there may be a close relationship between the distribution of natural resources of S. nudus and the distribution of water temperatures along the China Sea, assuming that the increase in number of the natural resource distribution of the worm from the North to the South might result from the change in water temperature.