In this study, on the basis of the grain size analysis using the laser diffract instrument and sieve-pipette methods for several model sediments, the two sets of grain size parameters are compared and the differences between the two methods are analyzed. The results obtained with Mastersizer 2000 show somewhat greater mean size and lower sorting coefficient than those obtained by the sieve-pipette methods. However, the results acquired by the two methods have significant linear relationship between the mean size and sorting coefficient. In comparison with the sieve-pipette analysis, the percentages of the most coarse-grained and fine-grained materials are relatively larger by the laser analysis. The regression analysis in different grain sizes indicates that the coarse  grained materials have better relationship, so it could be utilized for the data conversion between these two methods.