Abstract: Standard heat treatment and hot isostatic pressing(HIP) followed by standard heat treatment were conducted on a second generation single crystalsuperalloy DD6, and then high-temperature high cycle fatigue (HCF) test were carried out under the conditions of 850 ℃ and stress between 300 MPa and 850 MPa. The microstructure of the alloy in different states was observed, and the effects of HIP on microstructure and HCF properties of the alloy were investigated. The results show that, compared with the alloy only treated with standard heat treatment, the number and size of porosity in the alloy treated by HIP decreased obviously, the volume fraction of porosity deceased from 0.31% to 0.04%; its high cycle fatigue strengths increased from 331 MPa to 433 MPa, and its high cycle fatigue life raised sharply.