Abstract: In this paper, the modes of occurrence of Hg and As in three coal gangues were analyzed by sequential extraction procedure (SEP), aiming to provide the theoretical basis of removing mercury and arsenic in the process of power generation using coal gangue. The occurrence modes of As and Hg could be characterized as ion-exchangeable, carbonate-bound, iron-manganese oxide-bound, sulfides-bound, organic-bound and residual forms. The corresponding forms were obtained by adding different extraction solutions sequentially. The experimental results show that the sulfides-bound Hg and As are dominant form, accounting for 67.66%~72.68% and 56.71%~79.36% of the total Hg and As in the coal gangues respectively. The residual Hg and As are the second most abundant form, accounting for 23.70%~28.06% and 11.47%~18.02% of the total Hg and As in the coal gangues respectively. In addition, the content of the organic-bound As found in coal gangue is rare.