The diffractive optical element (DOE) is widely used to generate various illumination modes for pupil shaping optics in the projection lithography system. A mixed multi-region design method is proposed to calculate the phase of DOE, aiming at the poor spatial coherence of excimer laser. The DOEs generating conventional, dipole and quadrupole illumination modes are designed and analyzed by both the repeated multi-region design and the mixed multi-region design. Compared with the results of the repeated multi-region design method, the non-uniformities of the mixed multi-region design method can decrease from 26.45% to 1.12%, from 19.93% to 5.45% and from 17.93% to 3.54% respectively for the conventional, dipole and quadrupole illumination modes using the same local optimization algorithm. The analysis results indicate that the DOE designed by the mixed multi-region design can improve the uniformity of the far-field intensity distribution greatly while maintaining a high diffractive efficiency without changing the local optimization algorithm.