For precisely controlling the bias position of an electro-hydraulic vibration exciter, a scheme of a parallel mechanism of a two-dimensional valve (2D valve) and a servo valve is proposed. In the low frequency section, the mathematical model of the electro-hydraulic vibration exciter is simplified reasonably. A vibration central position is first analytically derived by assuming that 2D valve connected with parallel valve is equivalent to a single slide valve with neutral positive opening and the time-average flow rate through them is identical. And then the analytic solutions to excited waveforms superimposed on the bias position are further obtained. Finally, the experimental system is built to verify the theoretical analysis. The results reveal that this approximate analytical solution could describe excited waveform of bias control on electro-hydraulic vibration exciter. When the opening area of 2D valve is a constant, the bias position follows a linear relation with the throttling areas of the parallel valve which is no more than the maximum position. The excited waveform is close to the sinusoidal waveform. At the same opening area of the parallel valve, the bias position is reduced as the area coefficient of 2D valve increases. The proposed scheme not only ensures the frequency and the amplitude to be controlled independently but also the bias position to be adjusted precisely.