It is difficult to detect the crack quantitatively, because an error exist between the distribution of magnetic leakage field and the analysis result using standard crack theory due to the vast difference of the real geometry of cracks.The statistical analysis was carried out on 128 cracks with width below 50μm ,and a kind of combined crack was simulated,by which the magnetic leakage math-model of crack was set up.The testing results show that the relationship between the magnetic leakage and the geometry o...