Optical system and detection range of Synthetic Aperture Ladar (SAL) are analyzed. According to the imaging characteristics of SAL, the concept that SAL uses non-imaging diffractive optical system are proposed, meanwhile, the phased array model is introduced to analyze its performance. In the condition of using binary optical element on the feeder and primary mirror, the phaser parameters and beam pattern are presented using simulation. The signal of 2° view field is introduced into fiber with the 300 mm aperture telescope and compressed optical path. The radar detection range equation of SAL is introduced, coherent detection and signal accumulation gain are analyzed, the conclusion is SAL has good ability of detecting weak signal. Aiming at application requirement, system parameters and working modes of airborne SAL are given with high resolution and long detection range. With 5 cm resolution, the airborne SAL can achieve 5 km detection range with 1.5 km swath in strip-map imaging mode and 10 km detection range with 1 km swath in sliding spotlight imaging mode.