Tritium production rates were measured using a DT neutron source for solid breeder blanket mockups under conditions without and with a neutron reflector at Fusion Neutronics Source facility in Japan Atomic Energy Agency in our previous studies, and the experimental results were compared with the calculated ones. Uncertainties of the calculation results for the experimental condition with the reflector were larger than those without one. We have studied influence of reflector on calculation accuracy for tritium production rate in the present study. From the Monte Carlo calculation results evaluating the tracked path of each neutron, it can be clarified that the ratios of the tritium production due to neutrons scattered by the reflector to that due to all neutrons are 0.24 ∼ 0.57. The divergence of the ratio of the calculation result to the experimental one on tritium production from unity increases with the ratio of the tritium production due to neutrons scattered back from the reflector. It can be concluded that this increase is due to neutrons scattered by the reflector, and the calculation accuracy is enhanced by improving the calculation for back-scattered neutrons.