Abstract: In the last paper,Ik0, method was proposed for fission interference corrections. Another important kind of interferences in reactor NAA is due to threshold reaction induced by reactor fast neutrons. In view of the increasing importance of this kind of interferences, and difficulties encountered in using the relative comparison method, a parameterized method has been introduced.Typical channels in heavy v/ater reflector and No. 2 horizontal channel of Heavy Water Research Reactor in our institute have been shown to have fast neutron energy distributions(E>4 MeV) close to primary fission neutron spectrum, by using multi-threshold detectors. On this basis, Ti foil is used as an ''instant fast neutron flux monitor'' in parameterized corrections for threshold reaction interferences in our long irradiations. Constant values of (φ)/(φ)s=0.70±0.02% have been obtained for No.2 rabbit channel.This value can be directly used for threshold reaction interference correction in our short irradiations.