Industrial robot is applied for finishing complex craft with external signals. The PLC is used to control logic calculation between robot and external signals. Compared with traditional PLC, the soft PLC has characteristics of standard programming language, customized hardware configuration, etc. It can be directly embed in different control systems as interface. The soft PLC takes responsibility for logic control and I/O control. A new independent research controller was analyzed, and a soft PLC controller applied in industrial area was designed for this system. This soft PLC included programming module, compile module, execute module, monitor module. It could be applied for drawing LAD, generating IL, compiling executable file, running programs. The programming module and compile module were developed by Qt based on Windows OS. The execute module and monitor module were developed by Qt based on Linux OS.