Abstract: Through tensile test and fracture analysis, the reasons for unqualified elongation of biomedical CoCrMo alloy castings obtained by investment casting were analyzed. Combined with the theory of metal solidification, the corresponding improvement measures were proposed. The results showed that the main reason for unqualified elongation of CoCrMo alloy castings was the existence of a large number of shrinkage defects in castings. On the basis of strict control of melting and pouring process, the unqualified rate of castings was reduced from 9. 8% to 3. 1%.