The effect of alkali metal（AM）on crystallite structure of chars prepared by the pyrolysis of original and acid-washed coal without and with AM at 800—1050℃ in tubular furnace was investigated by XRD (X-ray diffraction) technique.The pyrolysis of coal samples and the gasification of chars were studied by PTGA (pressurized thermogravimetric analysis).The results show that both coal pyrolysis and gasification is affected by AM.At pyrolysis stage

the existence of AM inhibits the progress of char graphitizing

promotes the pyrolysis reaction and reduces its activation energy; at char gasification stage

AM is a catalyst

reduces gasification activation energy

goes up rate and prolongs the time to reach the maximum gasification rate.Modified random pore model can be used to describe the char-CO2 gasification process properly.