Abstract: This paper reports an ultraviolet laser four-framing shadow imaging system based on the laser with a pulse width of 16ns, a wavelength of 266 nm, a total energy of 30 mJ and a temporal resolution of 1.6 ns, which is used to study the transport laws of the interaction of Z-pinch generated plasmas with the plastic foam located at the center of the wire array and the main physical factors affecting the formation of the dynamic hohlraum. The high-energy and high-density laser beam is used to transmit through the plasmas. The spatial density distribution of the plasmas can be obtained by theoretically calculating the spatial intensity distribution of the laser beam after passing through the plasmas, which is diagnosed based on the plasmas absorption and attenuation characteristic to the laser beam. With the spatial density distribution of the plasmas, the laws of the early stability of the generated plasmas, pinch velocity, and so forth can be obtained. Experimental study indicated that plastic foam was compressed by the plasmas starting at about -25 ns before the X ray peak and was compressed to the minimum diameter at -5 ns before the peak. After that, the foam started to expand. At the X ray peak, the foam diameter was compressed from 3 mm to about 1 mm. The maximum compression ratio of the foam is about 9. The compression velocity measured by the experiment was about 3.3106 cm/s, and the unstable structure distribution of the magnetic fluid at different time is given.