A roll-angle error measurement method which can be integrated with other parameters measurement system is proposed. The light source, single-mode fiber-coupled laser module with thermo-electric cooler (TEC) is used to decrease the laser beam drift, and provide reference beam for accurate and stable measurement. A special prism is used as a sensitive part, and the roll-angle error is obtained through straightness error of the two beams from the special prism. The experimental procedures and results are presented. The results indicate that the system has good repetition and stability. Compared with electronic gradienter, the method for roll-angle error measurement is available, and the accuracy is about 2″.