Using the geomagnetic data of several great solar activities from Mar. 1988 to Mar. 1989 of 9 stations in China, and the equivalent ionosphere current systems of infinite plate current, we analysed the variation features of S_qfocus position of the mid-low latitudes in China and obtained reasonable explanation of S_qfocus variability corresponding to K_p, D_st, A_pindexes. It is showed that 1) In different K_pindex intervals, S_qfocus has different regularities. When K_p<4, S_qfocus moves to high latitudes as K_pindex is increased; When 4p<6, S_qfocus moves to low latitudes as K_pindex is increased; when K_p>6, S_qfocus is indistinct as K_pindex is increased.2) S_qfocus variation along latitude direction was mainly caused by ring currents, but variation along longitudinal direction was mainly affected by IMF sector effect.