The present invention provides an IP address allocation method for a master-slave network, an apparatus, and a system. A master device generates an IP address sub-segment group, and separately sends at least one IP address sub-segment in the IP address sub-segment group to at least one slave device, so that the slave device can use a received IP address sub-segment as a DHCP server address and allocate an IP address to a user device. In this way, the slave device can directly allocate the IP address to the user device, so that an IP address allocation time is reduced.