The invention relates to the technical field of optical amplifiers, and provides an assembly for dynamically performing optical time domain reflection detection and a detection method. The detection method includes the steps of acquiring signal light intensity detection signals of a first photodetector and a second photodetector, and when confirming that the signal light intensity in the second photodetector is less than a first preset threshold, sending a control signal to an L-band Raman pump so that the L-band Raman pump enters an optical time domain reflection detection mode; and when confirming that the signal light intensity in the second photodetector is greater than or equal to the first preset threshold, sending a control signal to the L-band Raman pump so that the L-band Raman pump enters an L-band Raman fiber amplifier operating mode. According to the invention, the L-band amplified Raman pump laser is made full use of, so that the Raman pump laser can participate in the L-band amplification and can also be used as an OTDR detection optical source, the product function is greatly enhanced, the product design is simplified and the product reuse rate is improved.