For the analysis of powder reaction rate, it is an important problem to discriminate logically the suitability between the reaction model and the experimental data. The conventional method means essentially an examination of the feature of the curve of conversion versus reaction time, for example to discuss the linear plot of the data. However, this method is irrational since the particle size distribution significantly deforms the feature of the curve. On the other hand, it is a logical judgment to inspect agreement between the data and the curve of the conversion versus reaction time calculated, by satisfying all the terms involved in the equations of the model. This judgment is especially favourable if the data are taken for a certain reaction system by using the samples with different conditions such as the average size, molar ratio and the size distribution.