In this paper the density of the demersal fish stock was considered as a compoent part of whole marine ecosystem. The data of fish caught were accumu-lated for about two years (23 monthe) and with 1,445 hauls. Materials were system-atically analysed by means of kolmogorov test of goodness fit hypothesis. It was foundthat frequency of distribution was closely related with the theoretical lognormal distri-bution. so we came to the primary conclusion that the index of catch density of thedemersal fish stock followed lognormal distribution. On this basis, we further deducedthat the stock density fillowed lognormal distribution as well. This discovery provideda suitable stochastic model for the study of quantitative distribution of the demersalfishes in the sea area.