Supercritical　water　gasification　(SCWG)　technology　shows　huge　advantages　to　achieve　efficient　and　clean　utilization　of　coal.　Ash　agglomeration　caused　by　K2CO3　addition　makes　ash　discharging　process　more　difficult　and　inhibits　gasification　reaction　of　carbon　in　agglomerated　ash,　which　prevents　the　constant　operation　of　the　system　and　decreases　gasification　efficiency.　This　study　investigated　the　formation　mechanism　of　ash　agglomeration　in　potassium　carbonate-catalyzed　SCWG　of　coal　and　find　a　solution　to　inhibit　this　problem.　Experiments　were　conducted　in　an　autoclave　to　figure　out　the　effect　of　K2CO3　(0　wt%-10　wt%)　and　Al2O3　(0　wt%-20　wt%)　on　ash　agglomeration　level　at　750　°C.　After　every　single　experiment,　solid　residue　was　dried　and　classified　into　different　sizes　(0–100　μm,　100–1000　μm,　＞1000　μm).　The　ash　agglomeration　characteristics　was　examined　by　X-ray　diffraction　(XRD),　scanning　electron　microscopy　(SEM)　and　energy　dispersive　X-ray　(EDS).　Results　indicated　that　K2CO3　reacted　with　clay　and　quartz　in　raw　coal,　then　formed　K2Si2O5,　KAlSiO4,　KAlSi2O6　and　KAlSi3O8.　K2Si2O5　plays　a　cohesive　role　between　different　ash　particles.　Adding　Al2O3　can　effectively　solve　this　problem　by　forming　KAlSiO4　instead　of　K2Si2O5.　Besides,　Al2O3　enhances　carbon　gasification　efficiency　by　increasing　heating　rate　of　feedstock　temperature.　Simulation　work　was　also　done　to　investigate　the　boundary　condition　for　ash　agglomeration.　©　2020　Elsevier　Ltd