Based on the tamping device with hydraulic excitation and independent clamping movement, an electro-hydraulic exciter composed of spin valve and micro-displacement double-functioned hydraulic cylinder is designed. Considering the working principle of the electro-hydraulic exciter, a theoretical model is established according to the two throttles principle and the related experiments are validated. According to the analysis of excited waveforms, the conception of saturation is first proposed. In addition, saturation of excited waveforms is analyzed and optimized through working frequency and axial length of orifice. The results indicate that the waveforms are approximately symmetrical because of inertial force and certain amplitude and slope of triangle wave, and sine wave and trapezoidal wave are achieved through adjusting suitable working frequency and axial length of orifice. Besides, axial length of orifice increasing or working frequency decreasing leads to increase of saturation. Saturation and axial length of orifice are nonlinearly related. Nonlinearity decreases with the increase of working frequency.