This paper aims to measure the neutron flux distribution over the cross section of the boron neutron capture therapy epithermal neutron beam at the Tsing Hua Open-pool Reactor (THOR) by using indirect neutron radiography. It is successfully performed using an aluminum plate coupled with an imaging plate (IP). The developed high-resolution image represents the relative distribution of the neutron flux across the aluminum plate. The horizontal profiles of 28Al activity, according to the measurement using IP and calculations using MCNP with different angular source distributions, were given. In addition, horizontal profiles of 56Mn and 198Au activities measured using AuAl and MnNi foils, respectively, were provided. From the comparison between the measurements and calculations, source angular characteristics of the beam were inferred.