Vibrating wire sensors are widely used to monitor the deformation of large civil structures, such as dams, bridges and nuclear power plants. The operating principle is based on a stainless steel wire excited magnetically into resonance by a coil. The wire excitation is a key point for improving the sensor performances. This paper deals with the wire response under the effect of the coil placed at different positions and supplied by different excitation signals. The resonant frequencies of a wire without or with bending stiffness are derived. For each resonant frequency, the influence of the excitation position on the wire vibration is investigated using Green’s function method. The theoretical analysis is experimentally verified by measuring the sensor response in the cases of continuous, short-pulsed and long-pulsed excitations. It is shown that improper excitation may lead to measurement errors. The optimal excitation mode for maximizing the excitation efficiency and inhibiting the high-order resonant frequencies is discussed.