The calculation of the doubly differential cross section was performed using sequential single charge exchange mechanism for the double charge exchange reaction 3He (π−, π+) 3n. The effect of the final state interaction between two active neutrons was investigated using Malfliet Tjon potential. Our results were compared with experimental results at intermediate energy range for the values 120, 180, 210 and 240 MeV. In this study, pion production was used to interpret the low energy peak that was observed on the forward angles at the incident energies of 210 and 240 MeV.