The microstructures of low carbon steel before, during and after rolling deformation of each stand were observed using optical microscope. The result showed that the microstructures were very fine after six passes rolling deformation. The effect of the first stand reduction on microstructure refinement was very distinct. During the rolling process, with the increase of the accumulated strain, the microstructures would further refine, and the density of dislocation would increase at the same time. In continuous casting thin slabs and each finishing stand, lots of observed precipitates were mainly A12O3 and MnS along the grain boundaries or in grains, which played an important role in the mechanical properties of the hot strips of low carbon steel produced by CSP (compact strip production) technology. The microstructures of low carbon steel before, during and after rolling deformation of each stand were observed using optical microscope. The result showed that the microstructures were very fine after six passes rolling deformation. The effect of the first stand reduction on microstructure refinement was very distinct During the rolling process, with the increase of the accumulated strain, the microstructures would further refine, and the density of dislocation would increase at the same time. In continuous casting thin slabs and each finishing stand, lots of observed precipitates were mainly A12O3 and MnS along the grain boundaries or in grains, which plays an important role in the mechanical properties of the hot strips of low carbon steel produced by CSP (compact strip production) technology.