The propagation pattern of the EH11 mode of waveguide HCN laser in free space is discussed and compared with the theory. In the near field, the intensity distribution is affected by the structural asymmetry of the laser, with some characteristics consistent with that calculated by Degnan; in the far field, the propagation of EH11 mode is approximated to the propagation of a Gaussian beam. Hence, the measurement of the laser propagation characteristics in the far field is the basis for the optical design of optical systems.