The invention provides an aligning and leveling method for main
machine guide rails of a
sizing and reducing
machine. The longitudinal levelness error and the transverse relative levelness error of each of the first guide rail, the eighth guide rail and the fifteenth guide rail are measured firstly, the levelness calculation value and the needed
gasket thickness are calculated, and the first guide rail, the eighth guide rail and the fifteenth guide rail are leveled; then the flatness error and the transverse relative levelness error of each of the first guide rail, the second guide rail, the third guide rail, the fourth guide rail, the fifth guide rail, the sixth guide rail, the seventh guide rail, the eighth guide rail, the ninth guide rail, the tenth guide rail, the eleventh guide rail, the twelfth guide rail, the thirteenth guide rail, the fourteenth guide rail and the fifteenth guide rail are measured, the levelness calculation value and the needed
gasket thickness are calculated, and the second guide rail is positioned with the first guide rail serving as the benchmark; and afterwards, the left thirteen guide rails are positioned and fastened in sequence, gaps between the top faces of all the guide rails and the bottom face of a horizontal rule are measured one by one, and it is ensured that the flatness of the top faces of the guide rails is qualified. By means of the aligning and leveling method, the working efficiency of guide rail replacing, aligning and leveling can be improved, the working time is shortened to 16 hours from the original 64 hours, the requirement for fast-tempo production is met, and the assembling precision of the guide rails of a main
machine C type seat of a
sizing machine and the quality of steel
pipe products are improved.