Abstract: To meet the requirements of the inertial confinement fusion (ICF) experiments on laser driver efficient third harmonic capacity, wu optimized the program for offline measurement of the crystal phase matching angle. The optimization measures include improving the ability for the collimation of crystal, and reducing the instability of measurement due to the output change of small diameter laser. Through theoretical analysis and systematic analysis of the actual measurements, high accuracies of offline measurement of crystal are obtained. Namely, the expanded measurement uncertainty of the second harmonic phase-matching angle is 15.94 rad, and the uncertainty of the tripler phase-matching angle is 27.8 rad.