In this study, the energy distribution of lost runaway electrons was primarily studied based on their bremsstrahlung emission in the experimental advanced superconducting tokamak (EAST) tokamak. The results indicate that the energy distribution of lost high-energy runaway electrons can be obtained with the deconvolution approach. The experimental results of the recorded bremsstrahlung emission in the EAST are presented in Sec. II. Then, the forward construction of the recorded spectrum is presented in Sec. III using the GEANT4 Monte Carlo simulation, and the backward reconstruction of the energy distribution of runaway electrons is presented in Sec. IV. The limitation of the results deduced in this paper is discussed in Sec. V. Finally, a summary is provided in Sec. VI.