The invention relates to a 
physical layer secure transmission method and 
system based on dynamic change of a 
channel encoding matrix, and belongs to the field of communication 
information security. The 
system comprises a joint 
encoder arranged on a 
physical layer of a transmitting end and a joint decoder arranged on a 
physical layer of a receiving end, and the transmitting end and the receiving end are communicated through a 
main channel. The method comprises steps as follows: a symmetric key obtained through key agreement is shared between the joint 
encoder at the transmitting end and the joint decoder at the receiving end on the basis of an existing 
key exchange protocol; a basic check matrix generated through optimized construction as well as a matrix extension factor is agreed publicly; joint 
encryption and error-control coding is performed on each transmitted 
plain text by the joint 
encoder, and corresponding code words in bit are obtained; the joint decoder 
decodes received code words into received plain texts at the receiving end. The method and the 
system can be used for realizing physical layer 
information transmission with high secrecy performance and high reliability.