Provided is a method for deviation amplification of a target nucleic acid sequence having a mutation relative to a wild type form in a sample, comprising: providing a single-stranded closed sequence complementary to at least a part of a sense strand and/or antisense strand of the wild-type form of the target nucleic acid sequence, wherein one or more locked nucleic acid substitutions are comprised in the closed sequence; providing a PCR reaction system comprising the sample, the closed sequence, and a forward and reverse primer designed according to the target nucleic acid sequence and performing a cyclic amplification reaction, wherein the denaturation steps comprise: raising the temperature to a sufficiently high temperature, contacting the closed sequence with the nucleic acid in the sample, and then cooling to a first temperature to make the closed sequence, the target nucleic acid sequence and the wild-type forming of the target nucleic acid sequence form a duplex, wherein the first temperature is higher
