According to the Huygens-Fresnel principle in the paraxial domain, an expression for the spectrum of polychromatic spatially coherent light in Young′s double-circular-aperture interference experiment in the far field is derived, and detailed numerical calculations are performed. It is shown that the number of the spectral switches on the oblique straight line with the y axis angle of 45° in the viewing screen is decreased with the increase of the central obstruction ratio of double-circular-aperture, and the distances among spectral switches on the line tend to be equal. With the increase of the central obstruction ratio, the distances among spectral switches at a fixed point on the straight line are shrunk. It is also shown that the spectrum on the x axis parallel to the double-circular-aperture center connection line is independent of the central obstruction ratio, and the distances among spectral switches are equal, changing the radius of the double-circular-aperture can control the number of spectral switches on the x axis. The spectral shifts and spectral switches on the y axis perpendicular to the center connection line depend on the location coordinates of the spatial points, the radius of the circular apertures and the central obstruction ratio of double-circular-aperture. With the increase of the central obstruction ratio of double-circular-aperture, the distances among spectral switches tend to be equal.