A method for preventing simultaneous issuance of two multicast flows, comprising a process of ceasing the transmission of a multicast flow upon an internet protocol set-top box (IP STB) being switched on; the ceasing of the multicast flow transmission can be initiated by the IP STB or by communication entities on the network side. The method provided by the present invention prevents simultaneous issuance of two multicast flows and thus eliminates unfavorable consequences of simultaneous issuance of two multicast flows, including picture quality loss and even abnormal restart of an IP STB, therefore the user experiences will be improved and user satisfaction will be distinctively increased.