Abstract: The minimum detectable limit of the nuclear radiation detector array is an important technic criteria to judge whether the detector satisfies the detecting requirements or not. From the qualitative point of view we know that，The detection of moving nuclear material is more difficult than that of static one (namely， the minimum detectable limit of moving nuclear material is lower than that of static one).This study adopts the Monte-Carlo general software—MCNP to compute and analyze the effect of movement of the nuclear matter on the minimum detectable limit of the nuclear radiation detector array.