PLC ladder diagram program development system and method

The invention relates to a programmable logic controller (PLC), in particular to a PLC ladder diagram program development system and method capable of conveniently achieving logout and logout removal of an instruction in a common PLC programming language-ladder diagram language, and the system and method are simple and convenient to operate and reliable in work. The system and method are characterized in that a flag bit of a control program is added, the explicit/implicit attributes of the flag bit in the control program are changed, parts capable of being complied and parts incapable of being complied in the control program are distinguished and displayed, and the parts capable of being complied are complied only. Compared with the prior art, the system and method have the remarkable advantages of simplicity and convenience for operation, high work efficiency and the like.