Abstract: Under two different experimental configurations, one with shield and the other straight incidence without any shield, time correlation coincidence counts of neutron between 252Cf fast ionization chamber and detector for uranium components with different masses, which induced by 252Cf fast ionization chamber, were calculated with Monte-Carlo method. Then the ratios of signal to noise in different simulations were roughly estimated in order to give some very important guidance on choice of experimental configuration. The results show that the ratio of signal to noise is proportion to the mass of uranium component under two experimental configurations. Additionally, the ratio of signal to noise under experimental configuration of straight incidence is greater than that of the other configuration.