Quantitative prediction of stress corrosion cracking (SCC) susceptibility and effects of key factors is critical for safe operation and lifetime management of light water reactors. In the present work, the effect of hardening on SCC of stainless steels in high temperature water environments was evaluated experimentally and theoretically for understanding irradiation assisted SCC (IASCC) and cold-work enhanced SCC. In the experiment, mill-annealed Type 304 steels were warm-forged to different yield strength levels and tested in simulated boiling water reactor (BWR) environment. Results showed that the specimen with higher yield strength exhibited higher SCC crack growth rate. Theoretical formulas relating crack tip strain rate and SCC crack growth rate to yield strength were derived, which indicate quantitatively that higher yield strength causes higher strain rate at SCC crack tip and so higher crack growth rate. The theoretical and experimental results are consistent.