Herein, a versatile parabolic band integrating mirror for a rectangular spot is proposed. A segmented parabolic equation satisfying the ultraprecision turning process is derived using an established segmented parabola homogenization model. Using the integrating mirror, homogenization width in the integrating direction larger than that of the traditional rotating segmental linear integrating mirror can be obtained, which is considerably larger than the input spot diameter. The influence of the number of integrating mirror segments on the uniformity of the output spot is analyzed. To avoid large deviation errors caused by a geometric method, the transmission equation for traveling Gaussian waves is used to calculate the defocused spot size in the rotation direction. Two integrating mirrors with output spots of 100 mm×3.2 mm and 14 mm×3.3 mm are designed and simulated by SolidWorks and Zemax, respectively, and the simulated spot sizes are 100.2 mm×3.2 mm and 14.2 mm×3.3 mm. The 14 mm×3.3 mm integrating mirror is processed and tested with a 3-kW fiber laser. The spot size is measured to be 14.3 mm×3.3 mm, and the uniformity of the homogenization direction reaches up to 90%, which satisfies the application requirements for laser processing.