Abstract: Solidification of micro-alloyed steels under different cooling processes was simulated by confocal laser scanning micros-copy (CLSM), and the change of the sample surface was in-situ observed. The correlation between the change of the sample surface and the precipitation of secondary phases was discussed. It is found that some small reliefs appear on the sample surface during liquid steel solidification. The appearing temperature and the distribution of reliefs are consistent with the results of the theoretical calculation of secondary phase precipitation and the characterization of transmission electron microscopy (TEM). The precipitation of secondary phases can be indirectly characterized by in-situ observations of surface reliefs, which will be helpful to analyze the effect of secondary phases on the evolution of the matrix.