Abstract: As the crucial stress component of cable bridge, parallel wire bundle would directly affect the safety of bridge structure. Based on the principle of magnetic flux leakage testing, the typical defects of parallel wire bundles are detected by using the flexible bridge cable detection sensor. The influence of the filling state of different parallel steel bundles on the magnetic leakage field of surface defects under circular and sector arrangement was studied by using point detection and line scanning. In view of the observed phenomenon that the filling of parallel steel wire bundles will reduce the magnetic leakage field strength of surface defects, a model for predicting the weakening law is proposed,and the magnetic leakage field distribution of surface defects at different positions was studied under the two states of filling with and without parallel steel bundles around the defective steel wire, and the relationship between the magnetic leakage field and the defect position under the two filling states was obtained.