This paper analyzed the twin-T notch filter circuit, deduced the expressions of transfer function, center frequency, bandwidth and Q value. Through calculation, analysis and simulation, the optimal resistance and capacitance were selected for the characteristics of wide field electromagnetic signal and the suppression requirements of frequency interference. Experiments show that the optimal design of twin-T notch filter's minimum depth of suppression is -31.9 dB when the bandwidth is only 3.62, so the application of the optimal design of twin-T notch filter can not only keep the desired signal, but also maximally filter out frequency and its harmonic interference noise in the wide field electromagnetometer.