A method for determining a designated forwarder (DF) of a multicast flow, a device, and a system are disclosed. In an Ethernet virtual private network (EVPN) scenario, a customer edge (CE) device is connected to a plurality of provider edge (PE) devices in a dual-homed or multi-homed manner. A first PE device is any one of the plurality of PE devices. After determining that the CE device connected to an Ethernet link joins a multicast group of a multicast flow, the first PE device determines bandwidth occupation statuses of a plurality of Ethernet links included in an Ethernet segment (ES) to which the Ethernet link belongs, and then determines, as a DF of the multicast flow based on the multicast flow bandwidth occupation statuses of the plurality of Ethernet links, a PE device corresponding to an Ethernet link that occupies lowest multicast flow bandwidth.