The optical properties of a SiOx film rapid-thermal-annealed RTA by CO2 laser are primarily investigated. The micro-photoluminescence -PL and HRTEM analysis indicate that the precipitation of random-oriented Si nanocrystals can be initiated when laser intensity Plaser larger than 4.5 kW/cm2. At Plaser of 6 kW/cm2, the Si nanocrystals exhibits a largest diameter of 8 nm and a highest density of 4.51016 cm-3, which emits strong PL at 790-825 nm. The micro-photoreflectance of the CO2 laser RTA SiOx film reveals a volume-density-product dependent refractive index increasing from 1.57 to 1.87 as the Plaser increases from 1.5 to 7.5 kW/cm2. Nonetheless, the laser ablation of SiOx film occurs with a linear ablation slope of 35 nm/kW/cm2 at beyond 7.5 kW/cm2, which terminates the enlargement of Si nanocrystals, degrades the near-infrared PL, and slightly reduces the refractive index of the CO2 laser RTA SiOx film.