A method for initializing an IP phone in an IP telephony system. The IP (Internet Protocol) telephony system includes an IP network; at least one gatekeeper connected to the IP network, having a DHCP (Dynamic Host Configuration Protocol) server and a TFTP (Trivial File Transfer Protocol) server; an IP phone connected to the gatekeeper for voice communication service; and an AAA (Authentication, Authorization and Account) server. The method allowing the IP phone to access the DHCP server via a DHCP server IP address, and allocating a terminal IP address and a TFTP server IP address to the IP phone; allocating subscriber information having a phone number and an IP address of the gatekeeper to the IP phone to allow the IP phone to access the gatekeeper and transmit a registration request signal to the gatekeeper; the gatekeeper informing the AAA server of subscriber information of the IP phone.