Embodiments of the present invention provide a method for transmitting uplink control information and an apparatus, applicable to a multi-carrier system. A user terminal receives physical layer signaling from a network device, where the physical layer signaling includes first indication information. The user terminal determines, according to the first indication information, a bit quantity of periodic CSI that can be sent on a channel resource or a piece quantity of periodic CSI that can be sent on a channel resource. The user terminal determines, according to the bit quantity or the piece quantity of the periodic CSI that can be sent, to-be-sent periodic CSI from periodic CSI corresponding to multiple downlink carriers. The user terminal sends HARQ-ACK information and the to-be-sent periodic CSI on the channel resource.