Potato late blight is a devastating disease which caused by Phytophthora infestans during the growth andstorage period. Up to now, PCR detection technology has become a routine way to detect the pathogen. In the presentstudy, nine detecting primers of Phytophthora infestans which have been published in China and abroad were usedto detect the specificity of Phytophthora infestans with other 5 common pathogens which also could infect potato byPCR technology. The results showed that both Primer-4-2 and Primer-5 have a good specific to distinguish thepathogen, and the specificity of other 7 primers was poor or not. Compared with these two primers, the specificity ofprimer-4-2 was better than primer-5, and it could give a good detection on different diseased samples included tu-bers, plant tissues and plantlets. The sensitivity of primer-4-2 reached to 10 pg/μL.