The invention discloses a prevention method and a prevention device for domain name system (DNS) denial of service. The prevention method for the DNS denial of service includes detecting a denial of service detection step and a denial of service prevention step when the DNS server is in a denial of service state, wherein the prevention of the denial of service is achieved through a cache curing function in the denial of service prevention step. A DNS denial of service prevention device comprises a denial of service detection module for detecting whether the DNS server is in the denial of service state and a denial of service prevention module for preventing denial of service, wherein the denial of service prevention module achieves the prevention of the denial of service through activating the inner cache curing function. According to the prevention method and a prevention device for the DNS denial of service, when the DNS server is in a denial of service state, the resource waste of a recursive parser of the DNS server is substantially reduced, and the resolution success rate of common domain names is improved.