Abstract: The duration and the interval of the pulsed source neutrons are two key timing parameters of PFTNA (pulsed fast/thermal neutron analysis) method. However, there are still no relative literatures about the evaluation and the setting of these two parameters, both at home and abroad. An function S was established to quantitavely evaluate the parameters, and then a theoretical model was proposed to obtain the optimal timing parameters. The calculation process was simplified by regarding the target object and surrounding mediums as a linear time invariant system. It was mathematically proved that the optimal duration and the interval had the equal value. The scenario of PELAN applied to landmine detection was chosen to expound the detailed calculation procedures based on the above-mentioned theoretical model. Furthermore, adaptability of the model to the surrounding medium and that to the detection layout were also fully tested. It was illustrated that, optimal timing parameters of the PFTNA method can be easily obtained through the theoretical model, meanwhile the model showed a strong adaptability to both the surrounding medium and the detection layout. Effective reference timing parameters could be provided when PFTNA method was applied to the fields like material analysis, contraband detection and landmine identification.