Abstract: Currently, research on the dynamic features of gas desorption mainly focuses on single particle size coal samples. There is less research on the dynamic features of gas desorption of mixed coal samples with different particle sizes. To solve this problem, a multi field coupled seepage desorption experimental system is used to mix coal samples with three different particle sizes (0,0.25) mm, 0.25, 0.5) mm, and 0.5, 1 mm in different proportions. Gas desorption experiments are conducted on mixed coal samples with different particle sizes. The changes in gas desorption kinetic parameters such as gas desorption amount, diffusion coefficient, and desorption attenuation coefficient are analyzed under different particle size coal sample proportions. The results indicate the following points. ① During the gas desorption process of mixed coal samples with different particle sizes, the main factor affecting the gas desorption amount in the early stage is particle size. In the later stage, the main factor affecting the gas desorption amount is the proportion of coal samples with different particle sizes. The larger the proportion of small coal particles, the greater the amount of gas desorption in the coal sample. ② The gas diffusion coefficient of mixed coal samples with different particle sizes exhibits temporal variability. As the gas desorption time increases, the gas diffusion coefficient decreases and eventually approaches 0. The initial gas diffusion coefficient decreases with the increase of the proportion of small particle coal. ③ The larger the proportion of small particle coal, the greater the attenuation coefficient of gas desorption. Therefore, in the process of underground gas content measurement, the proportion of large particle coal in the coal samples obtained should be increased as much as possible to reduce gas loss during the sampling process and improve the accuracy of gas content measurement.