A surge protection circuit, comprising: a surge protection unit and an interface, wherein the surge protection unit is electrically connected to the interface, the surge protection unit comprises an internal connection terminal block a first varistor, a second varistor, a third varistor, and one discharge tube, and the three varistors (12,13,14) are electrically connected to the internal connection terminal block, two varistors (13,14) of the three varistors are electrically connected to the discharge tube, and the discharge tube is electrically connected to the internal connection terminal block and is grounded, characterized in that the internal connection terminal block comprises a first internal connection terminal, a second internal connection terminal, a third internal connection terminal, a fourth internal connection terminal (L1p), a fifth internal connection terminal, and a sixth internal connection terminal; short connection sheets which are adapted to connect a part of the internal connection terminals together; and one end of the first varistor, one end of the second varistor, and one end of the third varistor (S 14) are electrically connected to the first internal connection terminal, the second internal connection terminal, and the fourth internal connection terminal (L1p), respectively; the other end of the first varistor is electrically connected to the fifth internal connection terminal, the other end of the second varistor and the other end of the third varistor are connected together and are electrically connected to the sixth internal connection terminal and to one end of the discharge tube, and the other end of the discharge tube is grounded. a surge protection unit and an interface, wherein the surge protection unit is electrically connected to the interface, the surge protection unit comprises an internal connection terminal block a first varistor, a second varistor, a third varistor, and one discharge tube, and the three varistors (12,13,14) are electrically connected to the internal connection terminal block, two varistors (13,14) of the three varistors are electrically connected to the discharge tube, and the discharge tube is electrically connected to the internal connection terminal block and is grounded, characterized in that the internal connection terminal block comprises a first internal connection terminal, a second internal connection terminal, a third internal connection terminal, a fourth internal connection terminal (L1p), a fifth internal connection terminal, and a sixth internal connection terminal; short connection sheets which are adapted to connect a part of the internal connection terminals together; and one end of the first varistor, one end of the second varistor, and one end of the third varistor (S 14) are electrically connected to the first internal connection terminal, the second internal connection terminal, and the fourth internal connection terminal (L1p), respectively; the other end of the first varistor is electrically connected to the fifth internal connection terminal, the other end of the second varistor and the other end of the third varistor are connected together and are electrically connected to the sixth internal connection terminal and to one end of the discharge tube, and the other end of the discharge tube is grounded.