Using radiation with a wavelength of 14 nm, Extreme ultraviolet lithography (EUVL) can reach a high resolution and remain relative large depth of focus, and it is a promising future-generation lithographic technique for manufacturing VLSI. EUVL operates in step-and-scan mode, and utilize all-reflective unobstructed reduction ring-field projection system. The starting configurations designing of unobstructed projection system is a nontrivial and important issue. A paraxial search method is introduced, which imposes constraints, such as rigorous telecentricity on the image side, quasi-telecentricity on the object, fixed magnification, Petzval condition and conjugated object-image. Curvatures of first mirror and last mirror, object distance and image distance are all solved consequently. And curvature of a reflecting surface coinciding with stop surface is solved. Paraxial search program is developed and some starting configurations are found. Two objectives are designed by optimizing two starting configurations. One is composed of four mirrors with the NA of 0.1, image field of 26 mm×1 mm, distortion of 10 nm, and the resolution better than 6000 cycle/mm. The other objective is composed of six mirrors with the NA of 0.25, image field of 26 mm×1 mm, distortion of 3 nm, and the resolution better than 18000 cycle/mm.