The invention relates to a phase measurement device of a beam splitter, which comprises a phase measurement device of an unpolarized beam splitter and a phase measurement device of a polarized beam splitter, wherein the phase measurement device of the unpolarized beam splitter comprises an unpolarized beam splitter to be measured, two polarized beam-splitting prisms, four photoelectric detectors and an oscilloscope; and the phase measurement device of the polarized beam splitter comprises a polarized beam splitter to be measured, two one-half wave plates, two polarized beam-splitting prisms, four photoelectric detectors and an oscilloscope. The phase measurement device can measure the phase relationship of two orthogonal components containing a vertical component (s component) and a parallel component (p component) of transmission light and reflected light of light waves after passing through the beam splitter. The invention is simple in measurement and easy to operate.