Abstract: The relative detection efficiency of neutron long counter was calibrated with ²⁴¹Am-Be neutron source. Energy conversion coefficient between 5.1 MeV and 14 MeV was also determined by the associated particle method. At the same time, the relative detection efficiency and energy conversion coefficient were calculated with Monte-Carlo method. In present work, the uncertainty of relative detection efficiency from experiment and calculation is 10.8% and 2.3%, respectively. Both are coincident in the range of uncertainty.