The invention provides a slidable supporting device used for an optical fiber preform cutting apparatus. The slidable supporting device comprises a frame, a positioning mechanism and sliding mechanisms mounted on the frame, wherein the positioning mechanism is mounted on a slidable supporting platform, and the sliding mechanisms are symmetrically arranged at the left and right ends of the slidable supporting platform; each sliding mechanism comprises a guide rail and two positioning rollers arranged on a same roller support; the guide rail is mounted on the frame through a guide rail supporting seat; two positioning rollers are arranged above and below the guide rail in a correspondence way and are slidable on the guide rail along an axial direction; the slidable supporting platform is mounted on the upper end of the roller support; and the positioning mechanism comprises a supporting assembly and a compressing assembly. According to the invention, the slidable supporting platform can steadily and smoothly move back and forth along the guide rail, so the quality of a cutting section is guaranteed; and through starting of a cylinder, the compressing assembly is driven to compress a an optical fiber preform, six degrees of freedom of the space of the compressing assembly are confined, so movement or rotation of the preform caused by cutting force during cutting is avoided.