Abstract: The time spectrum of all kinds energy neutrons and thermal neutrons, which resulted from the interaction between the formation and neutrons induced by the pulsed neutron source of the different pulsed width, are simulated by Monte Carlo Neutron-particles code. The time spectrum of thermal neutrons under the conditions of the different porosities, salinities and saturations are simulated. The linear relations between formation macroscopic cross sections and porosity, salinity and saturation are gained by the time spectrums, respectively. The results will lay the foundation for the study of PNN logging.