A method for indicating downlink control signaling and a related device are provided. The method includes: generating, by an access network device, indication information, and sending the indication information to a first terminal device by using downlink control signaling, where the indication information is used by the first terminal device to obtain information about an antenna port that is used by a second terminal device and that is corresponding to a demodulation reference signal, and the second terminal device is a terminal device currently performing spatial multiplexing together with the first terminal device. This implements interference detection performed by the first terminal device on a plurality of users.