The development of single-wire and multi-wire Z-pinches was investigated by X-ray backlighting using X-pinch as soft X-ray source. The experiments were carried out on the pulsed power generator PPG-I(400 kA/500 kV/100 ns) developed by the Department of Electrical Engineering of Tsinghua University. The X-pinch acting as the X-ray source and the single-wire or multi-wire Z-pinch acting as the object were installed in the place of a current-return rod or the center between the anode and the cathode. The X-ray films of high resolution and high sensitivity were used to record the results. The current sensor and Rogowski coil of our own design were used to monitor the current. In order to measure the mass ablation rate of the thin wire, the step wedge of micron-level thickness was designed. Through a large number of imaging experiments, the physical images of the plasma merging, the coronal plasma formation and the instabilities development of Z-pinch and some important parameters like mass ablation rate and core expansion rate were obtained.