This disclosure provides an information transmission method and apparatus and communication system. The method includes: receiving, by a user equipment, indication information transmitted by a base station indicating that the user equipment is capable of using the sidelink in a case where the air-interface link is incapable of normally transmitting data; and using the sidelink by the user equipment to perform data transmission with another user equipment in the case where the air-interface link is incapable of normally transmitting data. Hence, even if in a case where an air-interface link is unable to transmit data normally, data information may be transmitted successfully in other links.