Radiation monitors using Al2O3∶C as sensitive material have advantages of small size, high sensitivity, online remote annealing capability, etc. Accurately measuring OSL spectrum of Al2O3∶C not only helps to better understand the energy level distribution and luminescence mechanism of Al2O3∶C, but also guide the design of luminescence collecting and measuring system. Two different methods, direct measurement and dichroic measurement, are used to accurately measure the OSL spectrum of Al2O3∶C, and the results consistent with each other. The obtained spectrum has a peak shape, centered at ~414nm and with a full width at half maximum of ~62nm, and the long-wavelength side decreases more slowly. The broadband luminescence centered at 414nm (corresponding to energy of 3.0eV) is attributed to radiative transition from the 3P excited state to the 1S ground state of F-center. The dichroic spectrum measurement method designed can completely eliminate the influence of high-density reflected stimulating light, which can also be used in measurement of spectrum of other OSL materials.