An optoelectronic method of high-accuracy small-angle rotary measurement was introduced based on multiple-reflection between two plane mirrors, and an integrated experiment system was constructed. Then, the relationships between the system’s measure precision and measure range with laser beam reflection times in plane mirrors was studied. Finally, an actual application example was calculated and analyzed. The analyzed result shows that the measurement method has the characteristics of high precision and simple structure. When the reflection times are above 10, system measurement precision will reach 0.01 arc second. It provides a new method for sub-second accuracy level dynamic angle measurement.