  The Einstein's mass-energy relation $E=mc^2$ is one of the most fundamental
formulae in physics, but it has not been seriously tested by an elaborated
experiment, and only some indirect evidences in nuclear reaction suggested that
it holds to high precision. Manifestly, for a particle, different self
potential leads to different energy-speed relation, which can be used as the
fingerprints of them. In this letter, we propose an experiment to test this
relation. The experiment only involves low energy of particles and measurement
of speed, which can be easily realized. The experiment may shed lights on a
number of fundamental puzzles in physics.
