In this paper,we present a double-metal rectangular diaphragm based fiber optic accelerometer for seabed seismic detection application.We analyze sensitivity and resonance frequency of this sensor by way of mechanics of elasticity.The results show that the accelerometer can achieve an axis sensitivity of 45 dB re∶0 dB=1 rad/g,a cross sensitivity of about 30 dB between 10 Hz and 400 Hz,and the resonance frequency of about 820 Hz,which agree well with the theoretical analysis.In this system,the minimum measurable demodulation phase of the phase-generated carrier(PGC) is 10-5 rad/Hz1/2,and the minimum acceleration reaches 56 ng/Hz1/2 theoretically.With an all-metal structure,this type of accelerometer can better adapt to the special requirements of permanent deep seabed geophone.