The man-machine systems design is a major concern for the computer scientist, the control engineer and the ergonomicist. An adequate design for such systems means optimisation of their performance, which is the result of taking into account the human element since the design stage. Human integration, in the design stage, can strengthen the stability and optimality of all system functions. This paper deals with the problem of man-machine systems design by proposing a general approach based on system analysis methodology, action identification and action specification. All those aspects will be treated in this paper.