The invention discloses a method, a gateway, a PCRF network element and a system for dynamically assigning an IP address pool. The method comprises the following steps: when receiving a network attachment request of a user terminal, sending an assignment request to the PCRF network element, wherein the assignment request comprises user identification and user position information, so that the PCRF network element can assign the IP address pool to the user terminal according to the user identification and user position information, and returning the assigned IP address pool; and assigning an IP address to the user terminal in the PCRF network element assigned IP address pool. The PGW address pool is subjected to dynamic authorization management through the PCRF network element, thereby solving the problem that the address pool can carry out single distribution only based on APN or IMSI, and realizing dynamic user address pool allocation based on a position strategy and the like.