Relative parameters of nanosecond diffraction-free Bessel laser pulse were theoretically analyzed and measured in experiments. The expressions of the optical intensity distribution behind an axicon illuminated by a plane wave, maximum diffraction-free distance, minimum central spot radius were given based on the generalized Huygens-Fresnel diffraction integral theory. Relative parameters were also theoretically simulated and calculated. In the experiment, high stability nanosecond Bessel laser pulses were generated by using a Q-switched Nd:YAG laser with a plane-antiresonant ring (ARR) resonator and an axicon system. The pulse duration, maximum diffraction-free distance, optical intensity in the cross-section and minimum central spot radius were measured. Experimental results were consistent with the theoretical analysis. The fine structure of the optical intensity in the laser beam cross-section was presented by film-scanning, and the resolution of the beam pattern is much higher than that in a laser parameter analyzer.