Abstract: The principle of wear debris detector and the importance of magnetic field homogeneity are introduced. It is imperative to reach the inner magnetic homogeneity of the detecting coils so as to improve the sensitivity and reduce the measurement error originated from the changes of wear debris motion mode and flow model. Based on the radial and axial solenoid formula, the axial and external magnetic field homogeneities of the detecting coils are analyzed in detail. The mathematical model and optimized result indicate that the magnetic field in the inner wall of the detecting coils is of non homogeneity. At a ratio R/L <0.2, the magnetic field along the axial length and within the range of 90% radial direction is nearly homogeneous.It is thus supposed that the identification of the range of magnetic field homogeneity provides guidance to the design of induction transducer.