A frequency-doubling crystal is one of the most important light components in the inertial confinement fusion (ICF) facility. The principal section is closely related to the phase-matching angle and the absorption coefficient of the frequency-doubling crystal. To orient the principal section accurately, an indirect measurement method is presented based on light intensity. A measurement system was established using a laser, power stabilizer, half-plate, crystal, polarizer, and analyzer. The position of extinction, which was the principal section of the crystal, was obtained by rotating the polarizer and analyzer simultaneously. The Jones matrix model for the measurement system was deduced, and an expression formula for the relationship between light intensity, polarizer, and analyzer was derived. Through least squares curve fitting, the orientation of the principal section can be found. The validity of the model was verified using the simulation and experimental results. The test data show that the repeatability of orientation was better than 0.02°. The location accuracy of this method satisfies the requirements of KDP or DKDP frequency-doubling crystals in the ICF.