The physical models of local laser and signal laser are plane wave-Airy spot model or Gauss wave-Aiiy spot model commonly in heterodyne laser radar optics. In the case of plane wave-Aiiy spot, the radius of the photosensitive plane should be 0.79 times of that of the diffraction limit speckle of the optical system, the heterodyne efficiency is about 71% at this time. In the case of Gauss wave-Airy spot, the radius of the photosensitive plane should be 0.63 times of that of the diffraction limit speckle of the optical system and the heterodyne efficiency is about 81%.