Power transformer iron core earth current sampling circuit belongs to electric power power supply field, the utility model discloses a solve the current high problem of transformer core current fault misstatement rate. The utility model discloses the scheme: it is load output voltage that transformer T's secondary side passes through voltage stabilizing circuit, and sampling circuit includes that current transformer TA, LA25NP current sensor, fortune puts A1, NE555 time -base integrated circuit, auxiliary relay KA, 7805 steady voltage chips, rectifier bridge, resistance R1~R7, slide rheostat rp1, slide rheostat rp2, electric capacity C1~C4 and stabilivolt vs, auxiliary relay KA normally closed contact establishes ties among voltage stabilizing circuit's the interchange output circuit, earth fault takes place for transformer core, and its earth current increases severely, establishes ties in the disconnection of the KA normally closed contact of voltage stabilizing circuit outlet side, cuts off the return circuit for the power supply of secondary side load, just resumes the power supply after power line is normal.