Abstract: A structure for fixing a blind on a window or door frame, including two blind main bodies, four hinges, two connecting boards, two sets of decorative plates and four sets of auxiliary blocks. Each auxiliary block is a right triangular body formed with a longitudinal slot at a middle section. The slope face of the auxiliary block is disposed with a continuous stepped face. In the case that the middle gap between the two blind main bodies is too large after fitted with inner sides of the window or door frame, the auxiliary blocks can be reversely engaged and by means of moving the two contacting stepped faces, the engaged auxiliary blocks can be adjusted to have a certain width and then locked between the connecting boards and the inner sides of the window or door frame so that the gap between the two blind main bodies can be easily and quickly rectified to a suitable size.