Abstract: Monte-Carlo method for simulationg the responses of a dual-space neutron porosity oil well-logging tool is developed and presented.For practical computations,the specific Monte-Carlo code introduced here uses implicit capture、weight and energy cut off、geometric splitting and Russian roulette and directional biasing techniques as primary variance reduction methods.Some of the techniques have been improved partly.Numerical tests of practical examples are discussed and analyzed,which confirmed the effectiveness of these techniques.