This paper studied statistically the joint responses of magnetic field and relativistic (>0.5 MeV) electrons at geosynchronous orbit to 201 interplanetary perturbations during 6 years from 2003 (solar maximum) to 2008 (solar minimum). The statistical results indicate that during geomagnetically quiet times (HSYM > −30 nT, and AE < 200 nT), ~47.3% changes in the geosynchronous magnetic field and relativistic electron fluxes are caused by the combined actions of the enhancement of solar wind dynamic pressure (Pd) and the southward turning of interplanetary magnetic field (IMF) (ΔPd > 0.4 nPa and IMF Bz < 0 nT), and only ~18.4% changes are due to single dynamic pressure increase (ΔPd > 0.4 nPa, but IMF Bz > 0 nT), and ~34.3% changes are due to single southward turning of IMF (IMF Bz < 0 nT, but |ΔPd| < 0.4 nPa). Although the responses of magnetic field and relativistic electrons to the southward turning of IMF are weaker than their responses to the dynamic pressure increase, the southward turning of IMF can cause significant dawn-dusk asymmetric perturbations that the magnetic field and relativistic electron fluxes increase on the dawnside (LT ~ 00:00–12:00) but decrease on the duskside (LT ~ 13:00–23:00) during the quiet times. Furthermore, the variation of relativistic electron fluxes is adiabatically controlled by the magnitude and elevation angle changes of magnetic field during the single IMF southward turnings. However, the variation of relativistic electron fluxes is independent of the change in magnetic field in some magnetospheric compression regions during the solar wind dynamic pressure enhancements (including the single pressure increases and the combined external perturbations), indicating that nonadiabatic dynamic processes of relativistic electrons occur there.