A spectral analysis method for precisely measuring specific rotation of quartz is proposed. The measuring principle is analyzed by using the method of optical matrix. The result indicates that the specific rotation of quartz can be exactly calculated by measuring the transmittance curve of a sample quartz plate sandwiched between two paralleled polarizing prisms, and the correctness of the method is validated by a designed experiment using a spectrophotometer. The data is analyzed, and the rotary dispersion formula of quartz is fitted. Compared with Lowry’ formula, our formula is more accurate in visible spectral scope. Errors in the experiment is analyzed and the result shows that the measuring accuracy will be improved by choosing thicker quartz plate, longer wave band, lower scan speed, and smaller slit width.