A　new　method　to　study　the　characteristics　of　ash　layer　was　proposed.　Using　constant　temperature　thermogravimetry　technique,　the　kinetics　characteristics　of　coal　particles　(particle　size　3.0-4.5　mm)　were　analyzed　in　combustion　process　of　three　kinds　of　coal　particles　from　Fujian　Longyan,　Fujian　Yongan　and　Shandong.　Based　on　reaction　area　variation　and　shrinking　core　model,　the　total　resistance　of　combustion　process,　diffusion　resistance　and　combustion　reaction　resistance　were　discussed.　The　ash　layer　resistance　to　coal　particle　combustion　process　reached　its　peak　value　at　the　ash　layer　thickness　of　half　particle　radius.　The　experimental　results　and　analysis　show　that　the　resistance　of　gas　diffusion　through　ash　layer　of　particle　has　few　influences　on　the　particle　combustion　process　in　experimental　size　range,　and　the　max　ash　layer　resistance　in　the　particle　combustion　process　(ash　thickness　δ　=　R0/20.8-1.0　mm)　was　less　than　10　s/m,　far　less　than　the　reaction　resistance　of　the　combustion　process.