Metal detection machine is based on the principle of electromagnetic induction to detect metal, also known as eddy current induction. Generally, the metal detector is composed of two parts, namely, the conveyor part and the metal detector part, of which the metal detector head is the core part. The interior of the probe is composed of a group of transmitting coils and two groups of receiving coils. After the machine is powered on, the high-frequency electromagnetic field that can change rapidly is generated by the oscillation generator connected to the transmitting coils. When the machine is empty, the induced voltages of the receiving coils on both sides cancel each other before the magnetic field is disturbed, so that the magnetic field reaches a balanced state. When metal foreign matters enter the channel of the probe head, the magnetic field will be disturbed and changed, and the balance state of the magnetic field will be broken. The balance voltage of the two receiving coils will lose balance due to the voltage difference. The induced voltage that is not offset will pass through the signal receiver and be amplified by the control system to generate an alarm signal. The system can use the alarm signal to automatically remove the products containing metal foreign matters or send an alarm.