Abstract: The reasonable width of coal pillar is the key for ensuring safe production of fully-mechanized working face with double- roadway layout in the thick seam. To aim at the problems of coal roadway large-range breakage caused by unreasonable coal pillar dimension in Chahasu Mine, numerical simulation method was used for researching the reasons of the roadway instability and the reasonable width of coal pillar. The results showed that insufficient width of the coal pillar was the main reason leading to the abutment pressure superposition on the roadway two sides and the difficult maintenance of the roadway. Through the comparison of the stope stress, convergence deformation and plastic zone distribution under the condition of different width of the coal pillar, it was obtained that the reasonable width of the coal pillar in this mine was 35 m. The practice indicated that this scheme had significant technological and economical benefits.