The energy distribution of neutral particles emitted from STP-3(M) reversed field pinch (RFP) plasma has been investigated by a neutral particle analyzer (NPA) using a two-channel energy detector with the time resolution of 0.5μs over the whole duration of the discharge. NPA data show a high energy tail as well as the bulk ion distribution. It is found that the ion temperatures of bulk and high energy tail component have reached to the maximum before reversed magnetic field configuration, and that the tail temperature increases in the quiet period (QP). Furthermore, we found that the high energy ion density increases in both the relaxation period and the QP. The ion energy confinement time evaluated from magnetic reconnection model and the obtained ion energy spectrum is found to be about 720μs much longer than the electron energy confinement time 60-100μs, when ion heating mechanisms are discussed.