The invention discloses an adjustable fixing and splicing device for plate processing and a using method for the adjustable fixing and splicing device. The adjustable fixing and splicing device comprises a bottom plate, clamping mechanisms and a plate body; the two clamping mechanisms are connected to the top of the bottom plate and are used for fixing a plate body; the two sides of the top of thebottom plate is symmetrically provided with two first sliding rails; the first sliding rails are in sliding connection with first sliders arranged on the clamping mechanisms respectively; each clamping mechanism is composed of a cross beam, a lifting mechanism, a first slider, a first cylinder, a first extrusion plate, a first clamping plate, a second bolt hole, a first moving connection block, an F clamp, a cushion block, a fourth cylinder, a second sliding rail, a second moving connection block, a fifth cylinder, an extrusion rod, a fixed block, an ejector rod and an L-shaped connection plate; and the first sliders are fixedly connected to the bottoms of the lifting mechanisms and the bottoms of the sliding mechanisms respectively. The adjustable fixing and splicing device is convenientto adjust, is suitable for fixing and splicing plates with different widths as well as is high in plate fixing efficiency, accurate in fixation and convenient to operate at the same time.