The calculating method and equation of paralling modulation function curve of nonlineral crystal are applied in this paper, and verified experimeritally. The Half-wave voltage working curve of electron- optical crystal has been plotted. All kinds of modulation function curve and hystereosis loop in different conditions are tested. The result proved that the paralling method of modulation function curve of electron-optical crystal is an effective optical method of making half-wave voltage (Vπ) of nonlineral crystal.