Inductive magnetic sensor is the most widely utilized magnetic sensors in frequency domain electromagnetic（ FEM） method

generally it consists of inductive coil and pre-amplifier which is critical factor to affect performance of magnetic inductive sensor.In order to make inductive magnetic sensor to detect weak magnetic signals and deep underground

the preamplifier with broadband and low noise is required.The chopper preamplifier is designed and developed

based on the principle of magnetic flux negative feedback

and output noise of induction coil is inhibited effectively and both sides of the resonant frequency of induction coil have flat amplitude-frequency characteristic curve which broaden response band of inductive sensor.The performance

of magnetic inductive sensor is tested in shielded room

the frequency range is 0.001 Hz

10 kHz

and input noise is 3.75nV / Hz（1/2）

which guarantees performance for inductive magnetic sensor in real application.