It is highly desirable to increase the sampling rate of a fiber Bragg grating (FBG) interrogator in other to sense dynamic strains caused by impulsive acoustic wave. We have developed a wavelength interrogator featuring 100k samplings per second that consists of a solid-state spectrometer, a photodiode array and fully parallel read-out circuits. Central wavelengths on the reflected partial spectra corresponding to FBGs are calculated by the centroid method with the selected groups of the consecutive photodiodes at which each FBG spectrum is imaged. The centroid calculation is simple to be implemented in a field-programmable gate array (FPGA) and fast enough to capture impulsive strain waveforms in real time. Short-term noise on the interrogated wavelengths is estimated to be around 0.5 in terms of stain within the sampling bandwidth.