Abstract: Pinnotheres sinensis shen is very harmful to the cultivation of Mytilus eduis linnaeus. In order to limit or eliminate its distruction, we made threeyears of investigation on the habits and propagation characteristics of P. sinensis aswell as its danger to Mytilus edulis. Emphasis was placed upon the alternation ofgeneration of P sinensis. It was suggested in the paper that the present cycle ofartificial rearing of M. edulis be changed so as to avoid the great damage caused by Psinensis.