In this paper, a new universal design method of ultra-wideband (UWB) phase shifter on multimode resonators (MMR) is proposed and developed. The generalized topology of proposed phase shifters based on MMR is presented and their phase properties with J and K inverters are both analyzed. On the one hand, the phase shift performances are found dominated by the excitation of resonant modes, regardless of J and K inverters. On the other hand, the proposed 45° and 90° phase shifters can easily obtain bandwidth more than 110% with simple geometry and single-layer structure compared with other reported designs. The working principle and design method are given. Meanwhile, theoretical analysis of magnitude and phase shift bandwidth are carried out. Finally, a prototype of 90° phase shifter is fabricated and tested. The measured results well verify our design concept.