Shannon-Wiener diversity index is commonly used in measuring the community species diversity or assessing the ecological status of marine environments.There are two methods to compute the Shannon-Wiener diversity index in the surveyed region,which is calculated based on each sample data(Method 1) or based on the pooled data of the survey region(Method 2).In order to find out which method is better to reflect the species diversity of the survey region,as well as to examine the relationship between the Shannon-Wiener diversity index and the sample size,a comparative study of these two methods was carried out using simulation study based on the data from the macrozoobenthos survey in tidal flat wetland of northwestern Jiaozhou Bay in 2009.The results showed that the Shannon-Wiener diversity index calculated by Method 1 was lower than that from Method 2.The estimated Shannon-Wiener diversity index calculated by Method 1 was independent of sample size,and the Shannon-Wiener diversity index by Method 2 became greater with the sample size increasing,and then kept stable approaching the “true value” at the sample size of 20.Both the relative estimation error (REE) and the relative bias (RB) of the diversity index estimation from Method 2 were getting smaller when the sample size was greater than 20,which indicated that the sample size affected the calculating results of Method 2.Method 2 with enough or optimal sample size would be used in estimating the species diversity or in evaluating the ecological quality of the entire survey area,which would objectively reflect the status of species diversity in the survey area.