This study is to determine the width of coal pillar between roadways of the fully mechanised caving face with double roadways layout in a thick coal seam. The coal pillar between haulage gate and auxiliary haulage gate of the 4301 working face in the fourth panel was selected as a case study. Firstly, based on theoretical analysis, the pillar between roadways was along tendency divided into mining influence area, relative stability area and bolt supporting area after the first mining. The width of first mining influence area was 2.82 m determined by using the limit equilibrium theory, and the width of pillar between roadways was subsequently obtained as 7.83 m. Then, a numerical method was conducted to systematically simulate the laws of stress evolution, failure, and roadways deformation of pillars with the widths of 4, 6, 8, 10, 12, 15 and 20 m under the secondary mining influence. It is found that after the first mining, the high stress transfers from the coal wall to the pillar with the increase of pillar width. Besides, the definitions of the maximum and the minimum critical sizes are given. It is pointed out that the width of the narrow pillar should be less than the maximum critical size. By synthesising numerical results, theoretical results and principles of the pillar, the most favourable width of the pillar between roadways is suggested as 8 m. Finally, the rationality of the pillar width is verified by engineering practice. The results can provide a reference for the determination of narrow pillar between roadways of fully mechanised caving face with similar mining conditions.