The dual-species model is based on the Monte Carlo simulation conjoined with the embedded atom method (EAM) potentials. The model suggests that during relaxation of Ni3Al grain boundary，the trace element atoms can be seen not only as segregating species but also as inducing species. As segregating species the trace element atoms segregate (or enrich) to the grain boundary, but as inducing species they induce Ni atoms to segregate (or enrich) to the grain boundary. Evidently, the model can explain why the trace element atoms and Ni atoms co-segregate (or co-enrich) to the grain boundary. According to combination of positive (as inducing species) and negative (as segregating species) effects, the model explains the most obvious Ni-enrichment phenomenon at Ni3Al grain boundaries.