Based on the Huygens-Fresnel diffraction integral theory, the propagating properties of semi-Gaussian laser beams in free space are theoretically calculated in detail. Analytical propagation equations are derived, which permit us to study the intensity distributions of two-dimensional (2D) semi-Gaussian laser beams propagating in free space. The calculated results show that the propagation stability of semi-Gaussian laser beams in free space can be maintained well in the near field. As the propagation distance increases, the maximum intensities of the propagating laser beams decrease while the diffraction fringes gradually increase. At the same time, the width of the rising edge gradually grows. Finally semi-Gaussian laser beams become symmetrical beams. The better the symmetry is, the better propagation stability of semi-Gaussian laser beams will be.