The effect of magnetic field on the velocity distribution function of tritons in D-3He fuelled/field reversed configuration (FRC) plasmas is investigated. Some of the tritons produced by D(d,p)T reactions in the FRC are immediately andasymmetrically lost from the device without any interaction with background charged particles, and then non-symmetric loss causes a distortion of the velocity distribution function as well as a decrease in the number of trapped tritons. Using the distorted triton distribution, the 14 MeV neutron generation rate is estimated and compared with the values for Maxwellian plasmas (the effect of the magnetic field is neglected). It is found that in a typical ignited D-3He/FRC plasma, for example, Ti = Te = 80 keV, nD = 2n3He = 0.5ne = 3 × 1020m-3, τE = 0.5τP = 3 s, rs = 1.6 m and BW = 6 T, the reduction in 14 MeV neutron generation is about 20%.