Abstract: The mechanism of annulus reference block measuring integrated properties of magnetic particle testing was analyzed. A simplified mathematical model of magnetic flux leakage (MFL) was developed. The MFL of through hole in the annulus reference block was calculated by solving Laplace equation of scalar magnetic potential. The stress of magnetic particle on the annulus reference block was also calculated. Theoretical analysis indicates that ① the tangential component value of MFL on the center of through hole is maximum, and the normal component value is minimum. ② At the both sides of through hole center, the tangential component of magnetic partical stress is equivalent in value but opposite in direction. ③ Under the condition of constant diameter of through hole, with the increasing of through hole depth, the tangential component of surface MFL and magnetic partical stress both decrease rapidly. ④ Under the condition of constant depth of through hole, with the decreasing of through hole diameter, the tangential component of surface MFL and mgnetic partical stress both decrease rapidly.