Abstract: The data of IMF-B_z, auroral electrojet indices AL and ΔZ(the deviation of Z-component from geomagnetic quiet condition) near the equator during 1978-1988 are analyzed to discuss the solar-terrestrial coupling process. The results show that the 11-yearly variation of B_z is roughly corresponding to that of solar cycle activity. The variation of AL and ΔZ, however, are different. They are mainly controlled by physical processes in the magnetosphere and ionosphere. The international magnetic disturbed day(IMDD), chosen according to the A_p or K_p index, can represent the average level of the geomagnetic disturbance. The physical meaning of these indices, however, is nuclear. The disturbance level, the global feature presented and the physical process involved of IMDD from each month are different greatly. So, a new reasonable classification according to physical process is needed in futher study.