Abstract: Two-dimensional electric-filed vector is measured in this invention, wherein two linearly polarized laser beams are focused on two different bottom planes of an electro-optic crystal so that two reflected beams from the bottom planes have two different paths inside the electro-optic crystal and thus have different phase retardation when an electric-field is exerted on the electro-optic crystal by a circuit under test. The electric-filed direction of the circuit can be calculated by using two differential signals which are proportional to the phase retardation of the two reflected beams.