Abstract: Based on the total focus method (TFM) of imaging technology, the imaging examination and quantitative characterization of surface opening cracks on wind turbine main shaft were carried out. An array detection simulation model of wind turbine main shaft containing surfacebreaking cracks was established, and the TFM imaging detection was carried out using the simulation data and the total focus algorithm. Based on the solid directivity function of planar circular piston acoustic source, a compounding total focus imaging algorithm with bi-directional compensation and weighted by sign coherence factor was proposed, and the algorithm was verified using the simulation data. The results showed that the improved algorithm could effectively eliminate the artifacts and improve the imaging quality. Cracks on the shaft specimen were imaged and quantified. Moreover, the axial positioning error of the cracks is less than 2%, and the depth quantization error is less than 8%.