Class analysis is useful technique that can be used in many situations, from the syntaxes parsing, potential bugs finding, and unused code detecting to reverse engineer coding. In this paper, I write a small program classasm analysis the java class by calling the methods in ASM library. Here, the ASM name does not mean anything: it is just a reference to the “_asm_” keyword in C, which allows some functions to be implemented in assembly language. In Java, the ASM provides methods to read write and transform such byte arrays by using higher level concepts than bytes, that mean through the API in the ASM library we can analysis the class without reading the source code. ASM supply method to attract information from the compiled class file. In the research I use the simple company classes and the disconf-core-2.6.35.jar as examples, to show the results.