In order to improve the focal spot performance caused by continuous phase plate (CPP) in the laser facility for inertial confinement fusion (ICF) system, a theoretical calculation and analyse model for CPP with wavefront distortion is proposed, and off-line measurement system with three harmonic generation laser for the far-field intensity is built up according to the working conditions of CPP in the laser system. The comparison between calculation and measurement for the 330 mm×330 mm CPP and wavefront distortion component is carried out. The pattern and parameters are matched very well, so the correctness of calculation model and the credibility of measurement system are certified. The results show that the CPP′s focal spot performance is effected by the incident wavefront distortion severely. The CPP′s focal spot is changed largely when the disc of confusion caused by wavefront distortion is equal to half of the focal size caused by CPP. The changes include that the capacity usage ratio descends more than 4%, the focal spot radius increases over 20 μm, the super-Gauss order of the focal spot profiles reduces 1.3, the root mean square (RMS) value of inhomegeneity reduces 6%, and the percentage of side lobe increases over 0.5%.