To evaluate the release and transformation characteristics of different forms of Cl in coal gangue during combustion, the effect factors of combustion temperature, combustion time, and air flux were investigated using a small tubular furnace; the modes of occurrence of CI in coal gangue and its combustion residues under different temperatures were extracted with sequential chemical extraction; and the changes of matrix composition before and after coal gangue combustion were characterized by X-ray diffraction, X-ray fluorescence spectrum, and Fourier transform infrared spectroscopy. The results indicated, during coal gangue combustion under 120 min of combustion time and 90 mL/min of air flux, the organic matter, kaolinite, and ankerite were almost completely decomposed at 600 degrees C; the complete decompose for calcite and anorthite, for Elite and pyrite were at 900 degrees C and 1000 degrees C, respectively. Water-soluble Cl in coal gangue decreased greatly in 400-600 degrees C, with a decrease ratio of 12.02%, accounting for 82.05% of the total water-soluble Cl. CI-Fe-Mn oxides (Cl bound to Fe Mn oxides) were reduced all the time in 200-700 degrees C, with only 2.10% remaining in the residue at 700 degrees C. CI-organics (Cl bound to organics) was drastically decreased in 300-600 degrees C; in the residue after coal gangue combustion at 600 degrees C, the decrease ratio of this form Cl was 39.96%, accounting for 96.15% of its total Cl. In stages of 200-400 degrees C, 200-600 degrees C and 500-600 degrees C, some forms of Cl transformed into ion-exchange Cl, Cl-carbonate (Cl bound to carbonate), and Cl-residue which cannot be extracted by sequential chemical extraction, respectively. The release of total Cl in raw coal gangue mainly took place in the 200-700 degrees C stage: below 600 degrees C, the chlorine was mainly released in an inorganic form, with a small amount of organic Cl release; over 600 degrees C, the chlorine may be completely released as inorganic Cl, and the release ratio of total Cl was about 96.40%. The acid rain pollution caused by Cl from coal gangue during combustion should be concern.