Abstract: Theoretical and experimental investigation is introduced for the recent development of interference-fit strengthen technique. This paper will probe into the strengthen theory, in which the analysis of stress-strain field around the hole is put first, and point out the achievement obtained in the experimental investigation of strengthen effects and mechanism. The most significant benefit caused by the combined strengthen method of interference-fit and cold expanding (I-E) is briefly illustrated.The fatigue crack growth behaviour characters under cyclic load of samples with and without strengthening are compared and analysed. The clear difference of the crack propagation rate between the direction of thickness and the direction of (a) in the strengthened samples (dc/dN

Key words: intetference-fit strengthening, cold expanding of hole, cold-working fatigue.