To build a simple-lead Fetal Electro Cardio Graph(FECG) extraction system, a simple lead-based weak-signal programmable front-end amplifier design method is presented. The introduction of Automatic Gain Control(AGC) method can adjust the total magnification at the range of 10 000 when the output signal amplitude is relatively stable. The fitting of the relationship between the signal and magnification can be recorded automatically; the automatic gain range is up to 69 dB. This method can ensure that the details of the mixed-signal in the maternal abdominal wall will not be lost and will be easy to recover. Engineering application tests show that clear fetal ECG image can be obtained for fetal ECG extraction by using this amplifier.