In regard to the natural conditions along Zhejiang costal waters, the type and structure of sea-cage, the basic designing principles were proposed. In addition, its modular structure and design were discussed, which included area selection, cage type and array, farm scale, distribution density, arrangement of culture field, fish culture technology and environmental monitoring. Furthermore, making the culture practice at Qingshan zone of Xiushan island as an example, the experiment was carried on. The results indicated: the net cage that was used in this culture structure at this costal area was adequate for the 2.8kts maximal tidal current, with the enough ability of anti-wave property. The fish in this net cage grew fast, with little illness. The survival rate of fish can reach 95%. The influence on the cultured environment was unconspicuous. The chemistry index in the net cage culture area such as pH, D.O., COD and BOD varied 0.04, 0.18mg/L, 0.02mg/L and 0.06mg/L accordingly, compared with the control point of the uncultured area at the same time. Some kinds of nutrient salts in sea water were increasing, some were decreasing. The average amplitude is -0.034 to +0.017mg/L. Therefore, as far as cage culture is concerned, only by rational culture model design and its implementation, nice results can be obtained such as high landing, high effectiveness and less pollution.