Abstract: The extrusion force of a steel pipe is computed under a kind of a new polar coordinate system by the basis of upper bound method. The theoretical formulas for large scale steel pipes are proved by FEA method. One purpose of this paper is providing some bases for a specified load of extrusion press. When the extrusion ratio is less than 4, the deviations between theoretical results and FEA results are less than 10%. When the extrusion ratio is greater than 5, the deviations are less than 20%. Therefore the theoretical formulas are relatively adapted to predict the extrusion of steel pipes which have the extrusion ratio less than 4. For the large scale steel pipes, the extrusion force of a stationary mandrel structure is nearly equal to that of a following mandrel. On the contrary, for the small scale steel pipes, the extrusion force of a following mandrel obviously surpasses that of a stationary mandrel structure. Compared with other computational formulas on extrusion forces, the formulas in the paper are more accurate.