Nickel based 718 alloy is commonly used to fabricate grid springs for pressure water reactor, due to its excellent mechanical properties, relative ease of manufacturing, and good corrosion resistance. There is a risk of stress corrosion cracking (SCC) for nickel based 718 alloy in harsh environments such as irradiation, stress, and high temperature and pressure water in the primary circuit. In recent years, fuel rod damage caused by SCC of nickel based 718 alloy grid springs has emerged both domestically and internationally, which has a significant impact on the safety, reliability, and economy of nuclear power plants. Herein, the SCC initiation behavior of nickel based 718 alloy strips, being subjected to standard heat treatment, in a simulated pressurized water environment of primary circuit of nuclear power plant was assessed, while the evolution of crack initiation on the alloy surface was observed through intermittent sampling under different strain conditions. It is found that the cracking of 718 alloy emerged mainly on grain boundaries, meanwhile, the precipitates of (Nb, Ti)C tend to be oxidized into brittle Nb containing oxides. The oxidized (Nb, Ti)C and TiN are easy crack under the action of stress. With the increase of strain, cracks at grain boundaries and on particles (Nb, Ti)C tend to further propagating, and the cracks at TiN tend to expanding towards grain boundaries. Therefore, (Nb, Ti)C and TiN may play a detrimental role to the SCC resistance of nickel based 718 alloy.