Embodiments of the present invention provide a communication resource allocation method and apparatus, a terminal device, a base station, and a communications system. The method includes: sending, by a first network device, a resource request message to a second network device, where the resource request message is used to request a first communication resource, the first communication resource is a resource for sending a relay message to a third network device by the first network device, the resource request message includes first relay service type indication information, and the first relay service type indication information is used to indicate a type of a relay service to be performed by the first network device by using the first communication resource; and receiving, by the first network device, a resource configuration message sent by the second network device.