The digital TV broadcast system comprises: a TV program providing subsystem, a TV signal broadcast system, a network transmitting subsystem and a terminal play subsystem. Further, it can comprise a digital license authorizing subsystem used for providing the digital license for the TV program providing subsystem. Wherein the TV program providing subsystem further comprises a TV program digital signature device used for making digital signature for the video steam of TV program, and then adds the digital signature and digital license into the video stream transmitted in the network transmitting subsystem; the terminal play subsystem further comprises a security certification device used for examining validity of the digital license in the video stream according to its upper level certificates, and deciding if the video stream will be played or be rejected.