Since the transmitted signal of inverse synthetic aperture ladar (ISAL) has a very short wavelength, even the weak vibration of the target or the platform will seriously corrupt the ISAL image. In addition, existence of random phase error of the initial phases of the transmitted pulses of ISAL will greatly degrade ISAL images due to the limitation of the laser modulation technology, which also results in a defocused image of ISAL. The phase gradient autofocus (PGA) algorithm fails to compensate the phase errors induced by a high-frequency vibration; meanwhile, the spatial correlation algorithm (SCA) has a limited function on compensating the phase errors because of the relative rotation between the target and ISAL. Combining PGA and SCA, a new phase error compensation algorithm, which can be named PGA-SCA, is proposed. The effect of the relative rotation is eliminated by a circular shifting and windowing operation. Simulation results show that, the proposed algorithm is effective in correcting the phase errors and capable to generate a well-focused ISAL image.