The invention discloses nucleic acid and a kit used for detecting polymorphism of COX-1, COX-2 and GPIIIa genes as well as detecting method for detecting polymorphism of the COX-1, COX-2 and GPIIIa genes, and the method is strong in specificity, is high in sensitivity, is high in accuracy and is simple to operate. The detected results can provide guidance meaning for aspirin resistance. The detecting method provided by the invention adopts completely closed-tube operation, is simple to operate, is convenient and quick, obtains the detected results by directly detecting a fluorescence signal value in a PCR process, PCR post-treatment or electrophoresis detection is not needed, the problems such as easy pollution and false positive results in the conventional PCR technology are overcome, the nonspecific amplification problem can be effectively avoided, and therefore, the nucleic acid, the kit and the method are suitable for large-scale sample detection.