A far-infrared laser polarimeter-interferometer systembased on Three-wave technique has been established on the J-TEXT tokamak.The system determines Faraday angle by measuring phase difference betweentwo collinear, counter-rotating, circularly polarized laser beams, andacquires line-integrated electron density simultaneously by phase comparisonbetween the two beams and a third local oscilate (LO) beam. Three seperatelypumped HCOOH lasers at 432 μm are adopted as sources, suppling more than100 mW power output in sum. Parabolic mirrors are used to expand probe beamsto 450 mm wide, covering ∼ 80% of plasma cross section, which allowsprofile measurement with high spatial resolution. First experimental resultsof the polarimeter-interferometer have been obtained. 12 chords (3 cm chordspacing) simultaneous polarimetric and interferometric measurements areachieved, with phase resolution up to 0.1° at bandwidth of 50 kHz. Withthe high temporal and phase resolution, perturbations associated with thesawtooth cycle and MHD activity have been observed.