Abstract: The basic assumption in the derivation of the high temperature fracture mechanics parameters is the homogeneity of materials.However,the material inhomogeneity introduced by welding is inevitable in engineering practice.How to charcterize the creep crack growth with appropriate fracture mechanics parameters is rather challenging to the structural integrity assessment in the presence of weld interface.The infouence of material mismatch on the stress field and the time-dependent fracture mechanics parameters of uniaxial welded specimens is studied in the present paper.The applicability of conventional C^* equation based on the load line displacement is reexamined.It is found that under the extensive creep condition C^* value of hard weld/soft parent metal specimen can be significantly higher than that of single weld metal specimen,and the material mismatch has little infouence on C(t) in small scale creep in the studied cases.It is proposed that the C^* formula based on the load line displacement recommended by ASTM E1457 needs to be modificd to interpret the creep crack growth (CCG)behavior of welded specimens.