Cl- can affect the H2S adsorption, consequently affecting hydrogen absorption and sulfide stress cracking. The objective of this study is to define H2S surface coverage (θH2S) and use the developed θH2S to evaluate the influences of NaCl on the H2S-accelerated hydrogen uptake and the cracking susceptibility of C110 in sour environments. The θH2S description was defined using the inductance response (L) of EIS testing results. The positive correlation between hydrogen uptake fraction f and θH2S was developed based on the hydrogen permeation results and electrochemical impedance spectroscopy results. A negative correlation between KIC and θH2S was developed based on the notched tensile slow strain rate testing results at different H2S concentrations. This correlation was applied to predict KIC values in H2S environments with NaCl concentrations from 1 wt% to 20 wt%. The predicted and measured KIC values showed an opposite tendency as increasing NaCl concentrations. The measured KIC decreased with decreasing θH2S resulting from increasing NaCl concentrations. The fracture surface study explained this inconsistence, which revealed that the increment in NaCl concentration increases the pitting density on the steel surface, which lowers the energy required for crack initiation and propagation.