The embodiment of the invention discloses a method, a system and gateway and a domain name system for preventing network attack. The method comprises the following steps: the source request information and destination request information sent by a client end are received; the domain name system DNS selects the destination request information according to the source request information and notifies the client end; the source request information and the destination request information are checked; and if the checking result does not meet the requirement, the source request information and the destination request information are abandoned. The embodiment of the invention adopts the technical proposal that the DNS selects the destination request information according to the source request information sent by the client end and builds a corresponding relationship between the client end and a server according to the checking result so as to prevent the attack from DDOS.