The present invention discloses a ladder diagram matrix compiling and interpreting method based on a PLC. According to the method, the matrix operation of a ladder diagram is carried out directly without IL language conversion and interpretation. The method comprises a process compiling process and an interpreting process. According to the compiling process, since an IL language conversion process is omitted, only the simple scanning of the connection relationship of a matrix is needed, the ladder diagram compiling process is greatly simplified, fault points are reduced, and the compiling efficiency is improved. Since only the connection relation between elements in the matrix is processed in the compiling process, the complex AND OR and AND OR nesting logic are not processed, the logic operation process is simplified, the fault points are reduced, and the compiling efficiency is improved. In the interpreting process, the process of interpreting an IL language into a binary system index table is omitted, the scanning combination operation of the ladder diagram matrix is directly carried out, a lot of bottom layer CPU resources are saved, the program operating speed is improved, and the fault points are reduced.