This paper, with the securities industry as the research background, proposes a new method that uses XML to build a business knowledge base in the securities industry to automatically generate instruction. It studies the definition of data structures, how to create decomposition rule and use XML to describe the way of the values, how to create converter based on XSLT and so on. Practice shows that this method does not only simplify software development, but is also highly effective to carry out instructions decomposition. Based on this approach, knowledge platform and its corresponding reasoning process can be developed which is interactive and easy to expand for a variety of applications.