Abstract: Article use the t-test of single factors and triple levels to do analysis of variance with the slow determination ash content datas，which are achieved through three different particle sizes of pulverized coals，aiming to study The Influence of particle sizes to Ash Measuring. The results show that it not only will not influence the accuracy of Ash Measuring that modify particle sizes from 0.2mm to 0.25 mm, but also can save time，decrease power assumption，and absolutely promote efficiency.

Key words: ash content, slow determination, particle size, t-test