With the development of processing technology and the increasing requirement of spatial resolution, the slit widths of linear zone plate have become increasingly small. For slits with different widths on the linear zone plate, the incident uniform plane wave can excite one or more waveguide modes, resulting in inter-mode dispersion and phase differences. Even if there is only single-mode transmission in the slits, the effective refractive index of the fundamental mode is related to the width of the slit, which leads to phase difference of slits with different widths at the exit. To eliminate these phase differences, we propose an equal-width single-mode slit waveguide linear zone plate, study its focusing effect in the extreme ultraviolet band, and establish the corresponding Gaussian far-field analytical model. Numerical simulations based on finite element software confirm the distribution of the Gaussian mode field of fundamental mode, and a calculation based on the Fresnel diffraction integral further confirms the validity of the far-field analytical model. As one example, we design an equal-width single-mode slit waveguide linear zone plate and calculate its normalized one-dimensional light field distribution in the focal plane.