A terminal mechanism, comprising a terminal board, power supply connectors, and sealing rings; wherein, the terminal board is a flat board having an upper surface and a lower surface, and is provided with terminal holes thereon; each sealing ring is sleeved on a corresponding power supply connector; the power supply connectors are fixed on the terminal board through the terminal holes; and the sealing rings are in sealing engagement with the terminal board; each terminal hole is a ramped through hole with a variable cross-section; an annular lug boss is provided on each power supply connector; a lower surface of the annular lug boss is provided with an annular groove; a cross-section shape and a diameter of the annular groove are respectively configured to match with a cross-section shape and a diameter of the corresponding sealing ring; the corresponding sealing ring is disposed inside the annular groove; the cross-section of the corresponding sealing ring is circular; characterized in that: the terminal board is made of steel, and magnetic permeability μ of the steel is less than or equals to 1.31×10 -6 H/m; a part of the terminal hole, which is close to the upper surface of the terminal board, is a countersunk hole with a larger diameter, which is configured to partially accommodate a connector nut of the power supply connector and position the connector nut; an inner wall of each terminal hole comprises two stages of slopes, namely a first slope and a second slope; the first slope is disposed in contiguity with the countersunk hole, and a chamfer is made at a joint of the first slope and the countersunk hole; height of the first slope approximates to the height of the sealing ring; the sealing ring is in sealing engagement with the first slope; a first angle formed between the first slope and the upper surface is ranged from 77° to 79°, and a second angle formed between the second slope and the upper surface is ranged from 44° to 46°; and the cross-section of the annular groove is semi-circular; a depth of the annular groove is equal to or less than a radius of the cross-section of the sealing ring. the terminal board is made of steel, and magnetic permeability μ of the steel is less than or equals to 1.31×10 -6 H/m; a part of the terminal hole, which is close to the upper surface of the terminal board, is a countersunk hole with a larger diameter, which is configured to partially accommodate a connector nut of the power supply connector and position the connector nut; an inner wall of each terminal hole comprises two stages of slopes, namely a first slope and a second slope; the first slope is disposed in contiguity with the countersunk hole, and a chamfer is made at a joint of the first slope and the countersunk hole; height of the first slope approximates to the height of the sealing ring; the sealing ring is in sealing engagement with the first slope; a first angle formed between the first slope and the upper surface is ranged from 77° to 79°, and a second angle formed between the second slope and the upper surface is ranged from 44° to 46°; and the cross-section of the annular groove is semi-circular; a depth of the annular groove is equal to or less than a radius of the cross-section of the sealing ring.