A variable inductor (100, 200) being used to connect a first external component and a second external component, the variable inductor (100, 200) comprising: a primary conductor (110, 210) having a first node and a second node, the first node being used to connect the first external component, the second node being used to connect the second external component; a first secondary conductor (120, 220), magnetically coupling to the primary conductor (110, 210) to form a transformer structure with the primary conductor and first secondary conductor forming primary and secondary coils of the transformer structure and the first secondary conductor being disposed above or below the primary conductor; a first switch having two sides connected to the first secondary conductor (110, 220), respectively; wherein the first secondary conductor (110, 210) is formed by a single-loop structure with two changeable current paths (M, "M and P1") which are operated by the states of the first switch; a second switch having two sides connected to the first secondary conductor (120, 220), respectively, and the first secondary conductor (120, 220) is formed by a single-loop structure with four changeable current paths (M, "M and P1", "M and P2", "M, P1 and P2") which are operated by the states of the first and second switches (S1, S2); and a third switch having two sides connected to the first secondary conductor (120, 220), respectively, and the first secondary conductor (120, 220) is formed by a single-loop structure with eight changeable current paths (M, "M and P1", "M and P2", "M and P3", "M, P1 and P2", "M, P1 and P3", "M, P2 and P3", "M, P1, P2 and P3") which are operated by the states of the first, second and third switches (S1, S2, S3), whereby the inductance value of the primary conductor is changed as the equivalent inductance of the first secondary conductor and coupling factor are changed. a primary conductor (110, 210) having a first node and a second node, the first node being used to connect the first external component, the second node being used to connect the second external component; a first secondary conductor (120, 220), magnetically coupling to the primary conductor (110, 210) to form a transformer structure with the primary conductor and first secondary conductor forming primary and secondary coils of the transformer structure and the first secondary conductor being disposed above or below the primary conductor; a first switch having two sides connected to the first secondary conductor (110, 220), respectively; wherein the first secondary conductor (110, 210) is formed by a single-loop structure with two changeable current paths (M, "M and P1") which are operated by the states of the first switch; a second switch having two sides connected to the first secondary conductor (120, 220), respectively, and the first secondary conductor (120, 220) is formed by a single-loop structure with four changeable current paths (M, "M and P1", "M and P2", "M, P1 and P2") which are operated by the states of the first and second switches (S1, S2); and a third switch having two sides connected to the first secondary conductor (120, 220), respectively, and the first secondary conductor (120, 220) is formed by a single-loop structure with eight changeable current paths (M, "M and P1", "M and P2", "M and P3", "M, P1 and P2", "M, P1 and P3", "M, P2 and P3", "M, P1, P2 and P3") which are operated by the states of the first, second and third switches (S1, S2, S3), whereby the inductance value of the primary conductor is changed as the equivalent inductance of the first secondary conductor and coupling factor are changed.