Environmentally assisted cracking of 3.5NiCrMoV low alloy steel under cyclic straining was investigated in water environments at 60°C. Effects of strain range, strain rate, strain hold time and impurities in the water on the crack initiation life were investigated. The effects of long strain hold time up to 100 hours were studied and found to be especially significant. Lower strain rate, longer strain hold time and higher electric conductivity resulted in shorter crack initiation life. The corrosion current from the strained metal was measured in a simulated electrochemical system to clarify the root cause of the life reduction. Test results showed that higher strain range, lower strain rate, longer strain hold time and higher electric conductivity caused increased charge transfer, which caused shorter crack initiation life. A prediction model for the crack initiation life was proposed based on the charge transfer.