As an important part of the basic research on shock wave, shock reflection phenomena which appear in many practical situations, ranging from supersonic aircraft wings to hypersonic vehicles and engines, always receive a great deal of attention. Generally speaking, the slipstream which is an important part of shock reflection structures has a significant effect on the flow property. On the one hand, better understanding of the slipstream is beneficial to flow control which aims to reduce the stagnation pressure loss. On the other hand, it also provides a reasonable way in mixing enhancement. In view of these structures, the schlieren method and the shadow method are widely applied for flow visualization so far. However, the photographs which are obtained by the above methods merely reflect the flow field that is through temporal and spatial integration, rather than high-spatiotemporal resolution images. Also, the evolution of the slipstream cannot be fully investigated by means of the traditional methods of flow visualization. Garrison and Settles (1992) trace the evolution of the slipstream which emanates from the triple point of the k-shock system using the Planar Laser Scattering (PIS) technique. Afterwards, to describe the steady Mach reflection configuration approximately, Azevedo and Liu (1993) and Li and Ben-Dor (1997) investigate shape of the slipstream ignoring the viscous effect respectively. Then, Rikanati et al. (2006) indicate that the slipstream thickening of the pseudo-steady Mach reflection is caused by small-scale growth of the Kelvin–Helmholtz shear flow instability using the interferometry technique. Afterwards, Rubidge et al. (2013a, b; Rubidge and Skews 2014) point out that Kelvin–Helmholtz instability do form on the pseudo-steady Mach reflection slipstream, and describe the Kelvin–Helmholtz instability evolution using the schlieren images. However, little work has been conducted on the development of the slipstream in steady shock reflection. Hence, a series of experiments are performed to observe the fine structures of the steady shock reflection and investigate the evolution of the slipstream in this paper, using Nano-tracer Planar Laser Scattering (NPLS) technique.