Abstract: In order to quickly and accurately detect Cyprinid herpesvirus 2（CyHV-2） that causes the Crucian carp hematopoietic necrosis, two pairs of specific primers were designed according to the published CyHV-2 helicase gene sequence in GenBank. A nested PCR method for detecting CyHV-2 was established by optimizing the PCR annealing temperature. The specificity and sensitivity of the primers were tested, and 138 clinical samples of crucian carp were detected by using this method.The results showed that the optimal annealing temperatures for the first and second rounds of the nested PCR detection were 55 ℃ and 59 ℃ respectively. CyHV-2 helicase gene fragments of 515 bp and 277 bp could be amplified by this method, and could not be amplified for grass carp reovirus（GCRV）, cyprinus spring viremia virus（SVCV）, shrimp white spot virus（WSSV）, shrimp infectious subcutanized and hematopoietic tissue necrosis virus（IHHNV） and shrimp iridium virus（SHIV）. The detection sensitivity of CyHV-2 was 100～1 000 times than that of conventional PCR method. The clinical sample test results showed that the coincidence rate was 100%. The results indicated that the nested PCR method was highly specific and sensitive, and could be used for the early diagnosis of acute and latent infections of CyHV-2.