Due to the influence of the cogging structure，there will be cogging torque in the brushless direct cur? rent motor（BLDCM），which will increase the torque ripple and therefore affect the performance of BLDCM. To solve the above problems，BLDCM used in the Electro-hydraulic brake system（EHB）is taken as the research ob? ject，and the structure parameters are analyzed and improved to suppress BLDCM′s cogging torque. Firstly，by deriv? ing and analyzing the expression of cogging torque，it is found that its value is determined by basic structural param? eters and Fourier decomposition coefficients Br（nz/2p） and Gn Secondly，the function expressions of eccentricity，pole arc coefficient，auxiliary slot and Fourier decomposition coefficient are deduced respectively，and the relationship between them and cogging torque is obtained. Finally，the change of cogging torque is studied by finite element method under three conditions：the change of eccentricity，the change of polar arc coefficient and the addition of aux? iliary slot. The results show that when the eccentricity，polar arc coefficient and auxiliary slot shape are 7.90 mm， 0.74 and ellipse respectively，the corresponding peak cogging torque is reduced by 96.65%，90.48% and 86.74% re? spectively，and the cogging torque is obviously suppressed.