The solenoid collecting magnetic field optical transducing principle is presented to improve the operating stability of optical current transducer（OCT）. It is proved that the way to measure current by polarized light encircling conductor and that by polarized light threading solenoid axes are equivalent. The optical structure based on solenoid collecting magnetic field is designed based on the principle above. The experimental and continuous 25 months' field operating results of adaptive optical current transducer（AOCT） in the substation indicate that AOCT using the above optical structure can operate steadily.