Based on the finite-difference time-domain method, the optical forces between two ellipsoidal silver nanowires and the physical mechanism were investigated. The effect of the relative position and the dimention of two ellipsoidal silver nanowires on the optical forces were analyzed. A slight change of them would result in an obvious change of the optical force. The silver internal electrons were oscillated due to local coupling resonance. The plasma resonance would convert the photon energy in cavity into the kinetic energy of electronic collective oscillation. The electromagnetic field energy was reduced to negative state, which caused the contractive and negative optical force. Therefore, ellipsoidal silver nanowires attracted each other.