The provided is an adjustable single-channel time-domain sampling filter, a spectrometer, and a detection method. The filter includes N stages of cascaded asymmetric interference units, where each asymmetric interference unit includes: a first waveguide splitting element, arranged at the input end, for splitting input light into two output paths; two interference arms, which respectively receive the light output from the two paths of the first waveguide splitting element and have different arm lengths; and a second waveguide splitting element, for combining the output light of the two interference arms to generate optical interference. Among the N cascaded asymmetric interference units, at least three are provided with phase modulators on their interference arms. When in use, the adjustable single-channel time-domain sampling filter tunes the phase modulators located in different cascaded asymmetric interference units to form optical channels with different spectral responses in the time sequence.