In this study, a large size potassium deuterium phosphate (DKDP) single crystal with deuterium content of 70% was grown by traditional liquid phase method. The residual stress and micro-strain in the frequency tripling DKDP crystal were measured by neutron diffraction technique, and the micro-morphology of crystal in pyramidal and cylindrical faces were detected by X-ray synchrotron radiation. The distribution of macro-residual stress and micro-strain in the DKDP crystal sample along the ［100］ crystal direction were studied. The results show that the residual stress in the cylindrical region of DKDP crystal grown by traditional liquid phase method is compressive stress, while the residual stress in the pyramidal region is tensile stress. The tensile stress in the pyramidal region is easy to cause crystal cracking during growth and transportation, which is consistent with the experimental phenomenon. The residual micro-strain in the DKDP crystal grown by the traditional liquid phase method is small, however, there are still some defects in the DKDP crystal, which is one of the reasons for the existence of residual stress and strain in the crystal. The study can direct the engineering application of large size 70% DKDP crystal.