The behaviors of isovalent impurities doped in Czochralski (CZ) silicon crystal have attracted considerable attention in recent years. In this article, a review concerning recent processes in the study about germanium in CZ silicon is presented. The disturbance of silicon crystal lattice in and the influence on the mechanical strength due to germanium doping is described. Oxygen related donors, oxygen precipitation and voids defects in germanium doped Czochralski (GCZ) silicon has been demonstrated in detail. In addition, the denuded zone formation and the internal gettering technology of GCZ silicon is also discussed.