Time domain crosstalk in fiber Bragg grating Fabry-Pérot (F-P) interferometric hydrophone array system limits its practical application seriously. So it is necessary to analyze the generating mechanism of time domain crosstalk. With the phase generator carrier (PGC) demodulation, the effect of amplitude on phase is discussed for the interference signal. Then two comparative hydrophone systems with different reflectivities of fiber Bragg grating are fabricated and tested. Experimental results show that amplitude of the crosstalk is high for the demodulation signal with high reflectivity of grating (R=0.6), because the phase of the crosstalk signal hardly reduces on the basis of the PGC demodulation. On the other hand, the crosstalk has about 34 dB suppression with the low reflectivity of grating (R=0.02). Furthermore, the crosstalk in low reflectivity grating system is verified to be composite of the Doppler noise of precedent hydrophones and time domain crosstalk.