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The environmentally assisted stress corrosion cracking (SCC) behaviours of low alloy E690 steel in SO2-containing NaCl solution are investigated. The result shows that the corrosion on the metal surface becomes serious with the addition of NaHSO3, which mainly exhibits pitting corrosion. When the NaHSO3 concentration increases to 0.01 mol/L, the static load enhances the local AD resulting in the pits, and the stress concentrations around the pits leads to the initiation and propagation of the crack. And the SCC exhibits the transgranular cracking controlled by a combined mechanism of anodic dissolution (AD) and hydrogen embrittlement (HE). With the addition of NaHSO3, the corrosion potential on the surface of metal changes the crack growth rate through altering the pH and electrochemistry at the crack tip. Compared to the static load, the dynamic load promotes the dislocation accumulation, increases the electrochemical activity at the crack tip, which facilitates the HE and further accelerates the crack growth.