The invention discloses a control information transmission method. The method comprises steps: downlink control information is classified into public control information and special control information; a physical broadcasting channel is extended, and a public control channel domain is divided into multiple narrowband sub control channel domains through increasing position identifiers; before connection is built, public control information is sent to each sub control channel domain of the public control channel domain according to the position identifier; and after connection is built, according to the channel state of each sub control channel domain, special control information is sent to a sub control channel domain whose channel state meets a set standard. Through the set channel state selection scheme, when a base station sends downlink control information to a narrowband user terminal, a sub control channel domain with good connection quality and low load is selected, and thus control information transmission reliability by the narrowband user terminal in the control channel can be effectively improved.