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Estimation of the size structure of a fish population is often one of the primary objectives of an acoustic/trawl survey.The methods of estimation may be different with different sampling strategies.This paper describes the main results as well as the methods used during the acoustic survey of anchovy in the Yellow Sea in February 1999,with emphasis on the estimation of the number at length and biomass at length of the anchovy population surveyed under adoptive sampling strategy.The estimation is done for each transect.Within each transect,the biological sample data is weighted by fish quantity derived from the acoustic density (sA) of the echo signs that the biological sample represents.This method makes full use of the acoustic data available in a rigorous manner.It is essentially to estimate the size structure of each group of fish aggregation thought to having similar size composition.It is believed that this method may lead to a more accurate estimate of the size structure of a fish population surveyed under adoptive sampling strategy.