Beam′s oblique incidence and manufacture error of an axicon have a great influence on the quality of zero-order Bessel beams. Generally, the manufacture error is that the cross section of the axicon is not a circle but an ellipse. Based on the diffraction and geometry optics, the quality equivalence between the beam′s oblique incidence in a circular axicon and beams incidence in vertical angle in an elliptical axicon are analyzed. The diffractive optical patterns in oblique illumination on a circular axicon and the manufacture error in an elliptical axicon were simulated according to the calculation. The method to modify the influence on the nondiffraction Bessel beam of an elliptical axicon by rotating the axicon is proposed and the approximately perfect Bessel beams are obtained. The experimental result agrees with the theoretical analysis and numerical simulation.