In the framework of Keating model, the effects of the symmetric and asymmetric two-body and three-body interactions between surface and substrate atoms on the formation of asymmetric dimers of Si(001)2×1 surface are discussed.The symmetric interactions induce the symmetric dimers.The results show that formation of asymmetric dimers of Si(00l)2×1 surface is mainly affected by the asymmetric three-body interactions rather than the two-body interactions.