An in-line high efficient polarizer, composed of magnetic-ionic-liquid-adorned (MIL-adorned) hollow-core anti- resonant fiber (HARF), is theoretically proposed and experimentally demonstrated. The protocol is based on the selective conversion of polarization mode into leaky mode and attenuates quickly in MIL and the polarizer is featured by the magnetically tunable polarization extinction ratio (PER) and the thermally controllable operation bandwidth.