Abstract: Visualization of instantaneous density distribution has long been used to contribute to the understanding of complex flows. Using short pulse laser as illumination source, the visualization system of instantaneous density distribution was designed based on background orieted schlieren(BOS) technique. The laser pulse width is 10 ns. Experimental research was carried out with a non-axisymmetrical cone model in the Ф=120 mm shock wind tunnel. The instantaneous and long exposure schlieren images were obtained clearly under the condition of Ma=6. It is shown that the practical integral duration of obtained density distribution of the supersonic flowfield can be very short, as the effective exposure time of capturing instantaneous flow image is 10 ns, which is the pulse width of laser illumination. Compared to the long exposure schlieren images, the instantaneous images display more small time-scale details of supersonic shock flowfield. And it is found that even in a relatively steady shock flowfield during 1 ms, the instantaneous flowfield can be inhomogeneous and distributed with lots of isolated blocks. The experimental results indicate that the visualization system can reveal details of instantaneous shock wave flowfield. It is helpful for deeper study on complex flow mechanism. The visualization system of instantaneous density gradient distribution can be used in various kinds of supersonic or hypersonic flows.