To overcome the shortcomings of traditional techniques for non-intrusive debug and optimization, the on-chip trace system was adopted to record run-time information of embedded processor with special hardware. To fill the vacancy of former study, this paper gives a deep view of the mechanism, characteristics and applications of on-chip trace technique with TraceDo, an on-chip trace system of a multi-core SoC. The functions and structures of TraceDo were introduced, the working process of path trace was explained and trace applications were also discussed.