The chlorine content of fly ash in waste incineration affects its proportion in the cement kiln co-treatment of raw materials,so fly ash needs to be dechlorinated.XRD was used to study the existing speciation of elemental chlorine,which showed that chlorine existed in fly ash in two forms of water-soluble chlorine and water-insoluble chlorine.The water-soluble chlornde in fly ash of grate furnace were CaCl₂·Ca（OH）₂·H₂O,CaCl₂·2H₂O,CaClOH,KCl and NaCl,and the water-insoluble chlorine were Ca₁₀（Si₂O₇）₂（SiO₄）Cl₂（OH）₂ and AlOCl,etc. The water-soluble chlorine in fly ash of fluid-bed existed in the forms of CaCl₂·2H₂O and KCl and the water-insoluble chlorine existed in the forms of AlOCl,Ca₁₀（Si₂O₇）₂（SiO₄）Cl₂（OH）₂ and Ca₄OCl₆ and so on.The experimental results of water elution to remove water-soluble chlorine showed：for the fly ash of grate furnace,under the conditions of 10+4+2 of liquid-solid ratio（mL/g） and washing for three times at room temperature, the water-soluble chlorine removal rate could reach 97.01%;for the fly ash of fluid-bed,under the conditions of 6+6+4 of liquid-solid ratio and washing for three times at room temperature,the removal rate of water-soluble chlorine could reach 99.17%.Washing with acid and alkaline,high-temperature calcination could reduce the water-insoluble chlorine content of fly ash.The residual chlorine content of fly ash of grate furnace and the fly ash of fluid-bed after calcination were 0.36% and 0.45% respectively.