The invention discloses a media multicast method based on Web real-time communication and a media multicast system thereof. A WebRTC transmitting end encrypts media information to be transmitted so as to obtain the encrypted media stream and transmit the encrypted media stream to media broadcast equipment. In the media broadcast equipment, a virtual receiving end decrypts the encrypted media stream so as to obtain the media information and transmit the media information to a media distribution module. The media distribution module forwards the media information to the correlated virtual transmitting end. The virtual transmitting end encrypts the media information according to the pre-agreed encryption parameter so as to obtain the corresponding distribution media stream and transmit the distribution media stream to the corresponding WebRTC receiving end. The WebRTC receiving end decrypts the distribution media stream by using the pre-agreed encryption parameter so as to obtain the media information and realize media multicasting. The media stream generated by one WebRTC transmitting end is distributed to multiple WebRTC receiving ends through the media broadcast equipment so that multiple times of coding can be avoided and the multicast function of the media stream can be realized.