The design and fabrication of an optical 2×4 90° hybrid based on crystal birefringence for coherent receiver in free-space optical communication system are presented. The two pairs of balanced optical signals combined by the signal beam and local oscillator beam are output, which obtains the accurate phase difference of 90°, realizes 2×4 free-space hybrid, carries out photoelectric conversion and signal demodulation phase-lock. The 90° hybrid comprises two pairs of stacked birefringent plates, an analyser birefringent plate and a phase retardation plate. The testing results measured by heterodyne method verify that the 2×4 optical 90° hybrid can run accurately, effectively, stably and reliably. The phase compensation and further optimization schemes are also proposed. The free-space optical hybrid based on birefringence is particularly suitable for free-space coherent optical communication system, for intersatellite communications terminal for future compact, lightweight, low power consumption and high bit rate in the future.