An experimental study of high pressure water jet peening treatment on SPA-H and SPCC steel was conducted to study the effects of cavitation impacts of high-speed water on fatigue crack initiation and propagation of notched specimens. Pull-pull fatigue tests’ condition was 350 MPa maximum stress amplitude, 0.1 stress ratio and 10Hz frequency, while in-situ observation by SEM was employed. It was found that fatigue life of water jet peening treated SPA-H specimens has been obviously elongated by comparison with specimens without this treatment. However, for SPCC steel specimens, by comparison with those without water jet peening treatment, fatigue life was a little elongated, almost the same and obviously shortened corresponding to water jet peening treatment time of 5, 10 and 15 minute, respectively. High pressure water jet caused surface corrosion for SPCC low carbon steel, while with almost the same carbon content, copper, chromium and nickel elements increased anti-corrosion properties of SPA-H steel. These resulted in the different fatigue life of SPA-H and SPCC steel. In-situ observation on the crack tips approved above analysis.