This study investigates the effect of the environmental conditions (seawater mean thrust force and flow velocity) on a tidal turbine for different thicknesses mathematically. This had been achieved through predicting the fatigue stresses applied on the turbine for different conditions using Rainflow algorithm. The blades of the tidal turbine should be characterized by a low roughness to reduce eddies formation downstream the seawater flow. Fe-34.5Mn-l0Al-0.76C alloy had been selected in this study. Obtained results showed that, increasing thickness of the blade resulted in increasing the turbine lifespan for each studied flow velocity and thrust forces. However, increasing the flow velocity is predicted to increase the thrust forces due to the wake region formed downstream the flow leading to increase the fatigue stress on the blade. Consequently, the blade thickness should be optimized based on the geographical location decided to be installed by a turbine. As the geographical location effects on the environmental conditions significantly, which should be considered during the design stage to prevent fatigue failure of the turbine. Optimizing the blade thickness would help in maximizing the energy conversion efficiency of the turbine as well, as a lightweight blade would be able of generating electricity higher than heavy ones.