The invention discloses a straight pipe correcting platform and a straight pipe correcting method. The platform comprises a machine frame, a fixed head frame located at one end of the machine frame and a movable tail frame located at the other end of the machine frame. Vertical moving devices are arranged on the fixed head frame and the movable tail frame and comprise vertical sliding blocks and vertical sliding rails. The vertical sliding rails are dovetail grooves, the vertical sliding blocks are dovetail blocks matched with the dovetail grooves, and the vertical sliding blocks are connected with horizontal clamping devices. Each horizontal clamping device comprises a horizontal supporting block and a pair of clamping blocks clamping a flange. The horizontal supporting blocks are fixed on the vertical sliding blocks, dovetail grooves are formed in one faces of the horizontal supporting blocks, and the clamping blocks are provided with dovetail blocks matched with the dovetail grooves. The straight pipe correcting platform can quickly and precisely correct pipes according to the diameters of the pipes and the diameters of flanges, through the effect of the vertical sliding blocks and the clamping blocks, coaxiality of the flanges and the pipes is guaranteed, and automatic welding and evenness of filling materials are facilitated.