Based on Huygens-Fresnel diffraction integral theory and stationary phase method, the influence of the axicon with non-circular symmetry manufacture error on the zeroth order Bessel beam (J0 beam) is analyzed. The numerical simulation is compared with the beam patterns photographed by a charge coupled device (CCD) camera. Results show that if the cross-section of the axicon is ideally manufactured in circular symmetry, the field distribution behind the axicon is approximately an ideal Bessel beam. But if non-circular symmetry manufacture error exists, with the cross-section as an oval, the diffraction beam patterns will deviate the J0 beam. The greater is the difference between elliptical semimajor axis and semiminor axis, the larger is the deviation from the J0 beam. The experimental results fit the theoretical simulation very well.