A detecting system for detecting an under-test light of an under-test object includes a light spatial distribution unit, a chromatic-dispersion light-splitting unit and a detecting unit. The light spatial distribution unit is disposed on a side of the under-test object to receive the under-test light and form a plurality of point light sources. The chromatic-dispersion light-splitting unit is disposed on a side of the light spatial distribution unit to receive the point light sources and produce a light-splitting signal. The detecting unit is disposed on a side of the chromatic-dispersion light-splitting unit to receive the light-splitting signal and produce an optical field distribution of the under-test light.