The invention discloses a wireless relay transmission system based on security of a physical layer. The system comprises a central processor which is in electrical input connection with a signal source sending sub-system, and is respectively in electrical output connection with a terminal receiving sub-system, a relay transmission sub-system and a tapping sub-system; the relay transmission sub-system is respectively in electrical output connection with the terminal receiving sub-system and a video signal detection sub-system; when selecting the best relay node, the relay transmission sub-system selects the best relay node to assist transmission in the case of maximizing the capacity of a chain from a signal source to the relay node and maximizing the capacity area of a chain from the relay node to a terminal; the terminal receiving sub-system receives the signal source and a relay node signal, and combines the received signal source with the received relay node signal by using a diversity receiving technology, so as to achieve safe and reliable transmission from the signal source to the target terminal.