The invention discloses a variable-diameter assembly type sliding-mold platform of a sliding-mold system and belongs to the technical field of sliding-mode engineering. The variable-diameter assembly type sliding-mold platform comprises a central steel ring assembly, fixed-diameter radial-beam truss assemblies and variable-diameter radial-beam truss assemblies, wherein each fixed-diameter radial-beam truss assembly comprises a fixed-diameter upper chord, a lower chord, a first diagonal web member, a second diagonal web member, a first vertical rod, a second vertical rod, an end-part diagonal web connecting rod and a diagonal web connecting rod; the fixed-diameter upper chords and the lower chords are arranged in parallel from top to bottom; the right ends of the fixed-diameter upper chords and the lower chords are respectively connected to the peripheral edge of a central steel-ring truss; the fixed-diameter radial-beam truss assemblies at the periphery of the central steel-ring truss are in radial distribution; each variable-diameter radial-beam truss assembly comprises a variable-diameter upper chord, a variable-diameter vertical rod, a variable-diameter end-part diagonal web member and a variable-diameter diagonal web member; and the variable-diameter radial-beam truss assemblies are connected to the outer sides of the fixed-diameter radial-beam truss assemblies. The variable-diameter assembly type sliding-mold platform disclosed by the invention has the advantage that by replacement of the variable-diameter radial-beam truss assemblies, the effect of increasing or decreasing the diameter of the sliding-mode platform can be achieved.