Because it is difficult to accurately estimate the electric resistance of anisotropic conductive adhesive (ACA) joints, the ACA’s applications in high density packaging field have been greatly limited. The bulk resistance of particles is an essential part of the resistance of ACA joints. For the ACA using solid nickel (Ni) particles, because current flows along the spherical profile of the particles, the bulk resistance of these particles will be underestimated if the current bending effect is neglected. Here we propose a new method, which considers this current bending effect, to accurately evaluate the bulk resistance of Ni particles. First, a mathematical model to calculate the resistance of an arbitrary shaped resistor is deduced on the basis of electromagnetic theory. Second, a numerical model is introduced to calculate the potential distribution in the particles. Finally, the bulk resistance calculated by the new model is compared with the conventional methods. It is shown that the value obtained from this model is much higher than those calculated by other methods. Furthermore, the correlation studies between the bulk resistance and the particle’s diameter, the deformation degree, and the bonding force are carried out. And the results show that these three parameters influence significantly on the bulk resistance. In conclusion, to obtain accurate bulk resistance of ACA particles and make them stable and reliable, it is important to take the current bending effect into consideration and control the particle diameter and the bonding force properly.