The secular variations (SV) in g_1~0 of geomagnetic field, caused by the interaction between the geomagnetic field and the radial fluid-flow of the outer-core, are discussed with both statistical and analytic methods. When the value of g_1~0 s_2~0 is relatively high compared with other terms, SV in g_1~0 is characterized by exponential change. When the effect of non-dipole field is notable, SV in g_1~0 shows complex features. Especially when the value of g_1~0 is close to zero, SV in g_1~0 is completely determined by the random process of non-dipole fields. The secular variations (SV) in g_1 ~ 0 of the geomagnetic field, caused by the interaction between the geomagnetic field and the radial fluid-flow of the outer-core, are discussed with both statistical and analytic methods. When the value of g_1 ~ 0 When the effect of non-dipole field is notable, SV in g_1 ~ 0 shows complex features. Especially when the value of g_1 ~ 0 is close to zero, SV in g_1 ~ 0 is completely determined by the random process of non-dipole fields.