GraphViz package is a set of tools to describe, automatically layout and manipulate graphs, which is of great significance in connection and relationship analysis and illustration. The core module of GraphViz is the layout and render engines which generate neat and elegant visualization of graph in various common formats from a descriptive small language (the graph file language or the DOT language). This post will represent a brief introduction of the DOT language and show some applications that utilize the power of GraphViz.