The invention provides an optical power and gain detection device and method in an optical amplifier burst mode. The optical power and gain detection device used in an optical amplifier burst mode comprises a plurality of optical power detecting circuits, a FPGA device and a temperature detecting circuit, wherein each optical power detection circuit has the same structure and the realization mode, comprising a respectively independent photoelectric converter, a transconductance circuit, an analog signal conditioning circuit, a filter and an analog to digital conversion chip. Through the improvement of the analog circuit, the digital detection and the control in the conventional optical amplifier, and the using of the characteristics of the FPGA device, the detection of the optical signal and gain in the burst mode is realized by means of the algorithm. By means of the optical power and gain detection device and method in the optical amplifier burst mode, the addition of complex analog circuits is avoided, and meanwhile, the influence of the inconsistency of the components in the analog control scheme is avoided, therefore, the algorithm can detect the optical power accurately and steadily regardless of whether the optical signal is in the stable mode or the burst mode, and the range of application is wide; and the amplifier gain can be calculated more accurately by strictly controlling the synchronization of ADC sampling and the computing delay.