Abstract: In the combination exploitation of steam stimulation and steam drive, the cyclic steam cycles for converting into steam drive are of important effects on the recovery efficiency. The optimal cyclic steam cycles for steam drive are related with reservoir thickness, permeability, oil viscosity etc. and well spacing. In this paper, the factor of converting into steam drive (Cm) is defined on the basis of these influencing factors, and by analysis of 383 steam drive well groups in Karamay oilfield, the relational expression between the optimal cyclic steam cycles and the factor Cm is established, by which the optimal cyclic steam cycles for converting into steam drive of a reservoir or a well group can be determined