The invention relates to a plant supervision and a control system and an access control method. Because a structure that a plurality of CPU modules access to one I/O module is not supposed, the operations of all CPUs need to be specified. The control system is provided with a plurality of control modules which output generated control instructions according to operation instructions; and a plurality of input/output modules which outputs the control instructions received from the control module to a controlled object, and inputs the data inputted from the controlled object to the control modules. The control modules access to other control modules and input/output modules according to an access management list of accessable control modules and input/output modules.
