The invention discloses a spatial directional angle measuring system based on all-optical cross polarization modulation. The spatial directional angle measuring system comprises a first mach-zehnder intensity modulator, a polarization controller, a second mach-zehnder intensity modulator, a polarization controller I, an electric coupler, a microwave phase shifter, a polarization controller II, an optical fiber online polarizer, an optical band pass filter, a photoelectric detector, an offset T and a voltmeter, wherein the first mach-zehnder intensity modulator and the polarization controller are connected with a first laser light source; the second mach-zehnder intensity modulator and the polarization controller I are connected with a second laser light source; the electric coupler and the microwave phase shifter are connected with a microwave signal source; the polarization controller III, the optical fiber online polarizer, the optical band pass filter, the photoelectric detector, the offset T and the voltmeter are sequentially connected with the optical coupler. The spatial directional angle measuring system based on all-optical cross polarization modulation can be used for solving the problem of difficulty in quickly identifying antenna signal directional position information in an optically controlled phased array radar, and can be used for realizing primary measurement of an antenna spatial directional angle based on an all-optical cross polarization modulation method.