•A strain energy-based critical damage region is defined for fatigue modeling;•The effective strain energy density concept is utilized for fatigue analysis under notch and size effect;•A novel fatigue life prediction model combining weakest link theory with strain energy concept is proposed;•A general probabilistic procedure for notch fatigue modelling under size effect is presented;•Experimental data of GH4169, TC4 and TC11 alloys verified the model predictions accuracy. Notch fatigue analysis is vital for structural integrity design, while efficient fatigue models coupling notch and size effect are still lacking, which are highly desired for fatigue design of critical components. Accordingly, this study proposes a new probabilistic fatigue model for life assessment by combining the weakest link theory with strain energy concept. Specifically, a novel effective strain energy density concept is developed herein to build the connection between experimental data of smooth specimens and strain energy density of notched ones within the critical damage region. Experimental data of GH4169, TC4 and TC11 alloys with different geometries are utilized for model validation and comparison. Results indicate that the proposed model show higher accuracy than the other four models; in addition, the P–Wa¯–Nf curves describe the experimental data scatter effectively.