The invention discloses a common-optical-path point-diffraction synchronous phase-shift interferometer using lenses for light splitting. The interferometer comprises a testing optical path, a 4f system optical path, a light splitting optical path and a phase-shaft optical path arranged successively along the optical path. The testing optical path comprises a laser, a beam expanding system and a tested sample arranged successively in the common optical axis, and obtains measured information; the 4f system optical path comprises two Fourier-lens-and-reflector groups positioned in two arms of an interference system respectively, a linear-polarization pinhole diffraction plate is arranged in a confocal position of two Fourier lenses, and reference light and test light are obtained; the light splitting optical path comprises a lambda/4 waveplate and three light splitting lens groups, each of the reference light and test light is split into four beams at equivalent light path; and the phase-shaft optical path comprises a beam compressing system, a polarization array and a detector arranged successively in the common optical axis, and the light is received by the detector after beam compression, and four interference images are formed. According to the invention, pinholes are used for form spherical waves, the measuring precision is high, a common-optical-path system is included, the structure is compact and the anti-vibration performance is high.