The combined vision system concentrates the advantages of both the synthetic vision system and enhanced vision system, and provides improved image information via effective image fusion approaches, which will dramatically enhance the pilot爷s situational awareness with regard to the environment around the aircraft and thus further improve the flight safety. General consideration and design guidance are put forward for the combined vision system design, which include its function & performance, safety assessment & design assurance level, composition & architecture, human machine interface, layout & installation, and verification & certification.