Optical phase array scanning method is different from traditional mechanical scanning method as well as flat mirror, which can achieve inertialess random-access. AlGaAs waveguide optical phased array lidar has highlighted advantages in scanning speed, sweep range, etc. But the advantages bring difficulties in designing receiving system. Based on the AlGaAs waveguide phased array scanning lidar system, we design a direct detection and a heterodyne detection of the receiving system and analyze their characteristics of signal noise ratio. In the direct detection solution, in order to reduce background noise, multi aperture array receiving optical system is used. Aiming at the weak echo signal, we choose avalanche photo diode (APD) photoelectric detectors. In the heterodyne detection solution, for its large scan angle, we use the Airy method to achieve big angle coherent detection. Finally, the advantages and disadvantages of the two solutions are compared.