Cuprous iodide (CuI) is the ultrafastest inorganic scintillation crystal at present. But the low intensity of its ultrafast component luminescence limits the wide application of CuI at room temperature. In this paper, the photoluminescence (PL) characteristics of different quality CuI crystals before and after annealing in various conditions have been investigated in terms of peak position and peak intensity. The origin of different emission band peaked around 426 nm, 680 nm, 718 nm and 820 nm is discussed and the excitation spectra of two mainly emission bands is obtained. Meanwhile, the relative peak intensity of the ultrafast luminescence component to slow lumiescence component of CuI crystals has been studied with respect to the defect concentration of I vacancies. Especially, the method of improving the intensity of ultrafast compentent luminescence of CuI crystals is concluded. These results can provide an important reference for optimizing the luminescence performance of CuI crystals.