Polyculture experiments on Gracilaria tenuistipitata var. liuiZhang et Xia f. nov., Metapenaeus ensis De Haan, M. intermedius Kishinoye and Scylla serrata Forskal have been investigated and their results are as follows: 1. The optimum temperature and salinity for the seaweed growth ranges be-tween 17--30°Cand 17--29‰ respectively,and these are also suitable for growthofthe shrimps and the crab. The changes of water temperature and salinity in thefish pond are different from those in the coastal waters, which must be conside-red when the wild algae of Gracilaria is transplanted from coastal waters to fishpond. 2. The specific growth rate of this plant varies with water depths of seaso-nal replacement. The optimum water depths for Gracilaria growth in the fish pond are 20--50cm during months of January to April, 50--80cm of May to June,70--80cm of July to August, 35--70cm during September and 20--70cm of Octoberto December, respeetively. 3. The main nitrogen nutrient available for the uptake of Gracilaria is NH₄⁺,while the excreta from the shrimps and the crab contains much NH₄⁺. 4. Polyculture of marine algae and crustacea can promote growth each other,such as improving Water circumstance, increasing yield and more income, etc.Therefore,the polyculture is a good promising method for mariculture productionin coastal states.