A copy prevention method and apparatus for a digital video system is disclosed including the steps of: (a) adding a header area of a header start code and key field to a reproduced bit stream: stream; (b) decrypting and transmitting the bit stream to which the header area is added: added; (c) detecting a key field of the decrypted and transmitted bit stream and detecting copy prevention information; and (d) encrypting the bit stream according to information detected from stop step (c) and optionally recording it an on a tape.