In order to realize the large field, high resolution and dynamic measurement of optical component phase defects, we design a dynamic Twyman interferometer. Based on low-coherence laser and Michelson interferometer, a pair of orthogonal polarized light produced with phase delay is used as light source. By phase matching of the interference cavity, the phase delay between reference light and test light is compensated. The polarization camera is used to collect four interferograms with phase-shifting step of π/2, and the information of the phase defect is solved by phase-shifting algorithm. The effect of secondary diffraction on measurement results is analyzed based on the theory of the angle spectrum of plane wave. The influence of the polarizer error on the measurement results is analyzed by Jones matrix method. In the experiment, a laser-damaged optical plate is measured by this interferometer and Veeco NT9100 white light interferometer, and the relative error is 2.4%. In addition, this method is used to detect phase defects of optical flat in high power laser system, and the peak-to-valley value of wavefront is 199.2 nm. The results show that the interferometer can be used to detect phase defects of optical components, effectively.