A film dosimeter based on optically stimulated luminescence (OSL) material of CaS:Ce,Sm was developed for online irradiation dosimetry measurement. The stimulation is provided by a laser with a wavelength of 980 nm, and the OSL luminescenceis collected by a photodiode. Using (60)Co gamma-rays, we investigated the dosimetry characteristic of the dosimeter at different dose rates and total doses. The real-time detection results showed that the OSL signals versus total ionizing dose exhibited a good linearity in a dose range of 0.1-185 Gy.