Abstract: For the near-surface fatigue crack detection, the immersed non-collinear shear wave mixing method is investigated. The influence of interaction angle and frequency ratio on the nonlinear effect of mixing frequency is analyzed in different nonlinear source cases, such as material nonlinearity, water/specimen interface and fatigue crack. On this basis, the specimen with and without the near-surface fatigue cracks are scanned along the depth direction. The results show that there are significant differences in the characteristic patterns for different nonlinear sources, and the near-surface fatigue cracks of the specimen can be distinguished according to the peak of the longitudinal wave and its corresponding interaction angle. The water/specimen interface has a certain influence on the non-collinear cross-wave mixing detection of near-surface fatigue crack. The de-reference detection method can significantly reduce the influence of the water/specimen interface, and realize the effective detection of near-surface fatigue cracks.