The invention discloses an arc-aligning device and an arc-aligning method used between a crystallizer and a bending section of a continuous casting machine. The arc-aligning device comprises multiplepairs of rollers arranged on the two sides of the bending section, and further comprises an arc-aligning support and an arc-aligning plate; the arc-aligning support is arranged among the rollers at the two sides of the bending section, the arc-aligning support comprises a bottom plate, inclined wedges and a bottom plate positioning backup plate, the bottom plate is arranged to be in a rectangularshape, a guide positioning groove for allowing the arc-aligning plate to penetrate through is formed in the longitudinal central position of the bottom plate, a pair of inclined wedges are arranged and are symmetrically arranged at the parts, on two sides of the guide positioning groove, of the upper surface of the bottom plate, a plurality of hoisting holes are formed in the bottom plate, and thebottom plate positioning backup plate is arranged at the rear end of the lower surface of the bottom plate; and the arc-aligning plate is arranged to be in a rectangular strip shape, a hoisting holeis formed in the upper end of the arc-aligning plate, and a pair of symmetrical arc plate supporting shafts are further connected to the two side faces of the arc-aligning plate. According to the arc-aligning device and the arc-aligning method, during arc-aligning operation, a person does not need to enter the bending section, meanwhile, the arc plate can be automatically attached to the surface of the roller needing to be measured, the operation efficiency is improved, and the arc-aligning operation of straight and bent sections can be safely and quickly carried out.