Abstract: The collagen fibres of the bodywall from Asterias amurensis form a three- dimensional orthogonal web.Voids in the web contain ossicles and papulae. The inorganic substance is mainly calcium.In order to extract collagen from A.amurensis bodywall,inorganic layer should be detached first. Optimization and changes of bodywall during the process of decalcification was studied.Changes under influential factors were described.These factors included concentration of hydrochloric acid,solid- to- liquid ratio,and decalcification time. On the basis of single factor experiment,the results by orthogonal experiment show that the optimal conditions were hydrochloric acid concentration 1.0 mol / L,solid- to- liquid ratio 1 ∶ 10,and decalcification time 21 h. After the decalcification,the de- calcification rate can reach to 73.85%.After the decalcification,the bodywall became thin and soft.The internal structure became loose and rough.As the decalcification went on,hydrochloric acid gradually penetrated into the internal structure,metal ions diffused from the inside.