The testability of the optical guided-wave beam deflector has been demonstrated for the first time. For this, the Gaussian function model of the modulation characteristio curve is presented by where I is the sampling output light intensity, and Im is the maximum of I. D is the normalized coefficient of the sampling detection, and Ds is the contribution from the background light in D. V is the modulating voltage, and Vm is corresponding to I = Im and D = l. Vd is used to represent the width of the d V curve. Theoretical analysis using this model agrees with the measured results basically.