The electrostatic interfacial adhesive force acting on a spherical toner particle on a photoreceptor surrounded by a continuum toner layer was investigated. As the electric field of the toner layer is non-uniform, the variation in toner charge and the induced dipole and quadrupole moments on the spherical toner particle were obtained. The interfacial electrostatic force was calculated using the multiple effects of the mirror charge and the induced multiple mirror moments on the particle. The total interfacial force was obtained by adding a van der Waals force, as determined in relation to experimental results, to the electrostatic force. The efficiency of transferring a toner particle in intimate contact to paper saturated in the static state above a certain transfer voltage in the electrostatic transfer process. In the dynamic state, multiple phenomena related to toner particle transfer efficiency (saturation, plateau, peak, and impossible of detachment) were explained by the influence of toner charge. These phenomena resulted from variations in the threshold detachment field due to variations in the toner charge. It was shown by centrifugal experiment, that the force depends on R^2.2 for radius, R, of toner particle, and these results explain various experimental observations on the electrostatic transfer process.