  We propose a decaying cold dark matter model to explain the excess of
electron recoil observed at the XENON1T experiment. In this scenario, the
daughter dark matter from the parent dark matter decay easily obtains velocity
large enough to saturate the peak of the electron recoil energy around 2.5 keV,
and the observed signal rate can be fulfilled by the parent dark matter with a
mass of order 10-200 MeV and a lifetime larger than the age of Universe. We
verify that this model is consistent with experimental limits from dark matter
detections, Cosmic Microwave Background and Large Scale Structure experiments.
