Abstract: Based on the Fresnel-Kirchhoff's integral theory, the three-dimensional near filed and far filed light intensity distribution of non-chain pulsed DF laser with unstable resonator was obtained using Fast Fourier algorithm. Numerical calculation shows that the mode pattern is ring shaped at near field and multistage diffraction ring with central bright spot at far field,and the near field spot laser intensity will be concentrated as M increases, while the far field angle of divergence will increase with the increment of effective Fresnel number(Neq). Then the influence of mirror tilt on near-field light intensity distribution is investigated, indicating that the beam in near field will be deteriorated when misalignment appears, the larger of the tilt angle the much more obvious of asymmetric light distribution. The measured light intensity distribution on near-field and far-field and the variation of near filed light intensity distribution with mirror tilt angle are consistent with the simulation results, and the far-field divergence obtained is 1.2 mrad. The simulation results can provide a basis for cavity mirror misalignment diagnostic analysis and resonator regulation of non-chain DF laser.