Abstract: A two-frame laser differential interferometer system has been developed, with which two high-definition interferograms with an interval of 3 ns-12 ns can be obtained in one shot. The system generates two probe pulses with certain intersection angle and time interval via a beam splitting and delaying device. A special off-axis four-focus imaging system is used to image the object on two different areas on a single CCD ship. The system is applied to aluminum wires Z-pinch experiments. Interferograms of Z-pinch plasma evolution are obtained, including wires expanding and ablation, generation and evolution of corona plasma and precursory plasma, etc. Electron density distributions of early-stage Z-pinch plasma are calculated from the interferograms.