Abstract: The investigation on gonad index of sea urchin, \%Strongylocentrotus nudus\% in Dalian in a whole year and histological observation on the gonad development of the sea urchin showed that the natural spawning of \%Strong ylocentrotus nudus\% occurred from the end of July to late September in Dalian, peak time being from mid August to early September when water temperature decreased from 22℃ to 20℃ The male matures a little earlier than the female does The gonad maturation was from July to August, and the gonad atrophy was from October to April. The optimum capture duration of \%Strongylocentrotus nudus\% is from June to early August