A kind of resonator with spatial-temporal phase modulation is proposed. The modes of this kind of resonator are analyzed and calculated numerically in terms of the modal theory of coherence in space-time domain. The results show that the modes are completely coherent under fixed phase modulation on one mirror of resonator. There is a suitable value of resonator parameter to obtain flat-top beam on one mirror. For resonators with random disturbed phase mirror, its modes are partially coherent, and there also exists a suitable parameter to get flat-top beam.