The creep-fatigue (CF) response of 316H steel base metal (BM) and welded joint (WJ) as a function of holding time, along with corresponding deformation mechanism and failure mode are studied. The CF response of both BM and WJ exhibits initial hardening followed by gradual softening. Correspondingly, the hardening degree of BM is higher than that of WJ, while WJ has a faster softening rate, which is due to their different initial microstructure and microstructure evolution during the cyclic process. Due to the enhanced recovery process, the deformation mechanism changes from primarily planar to wavy slip, which explains the difference in cyclic softening. With the increase in holding time, the nucleation and growth of intergranular cavities and cracks lead to the transformation of the failure mode from transgranular to intergranular. The failure location of WJ occurs in the WM region, and the ferrite transformation plays an important role in the initiation and propagation of cracks. [ABSTRACT FROM AUTHOR]