Particle contamination of poly-Si films deposited in an LPCVD system was investigated by using the orthogonal array L8 experiment. Gas injection, temperature, pressure and flow rate were used as variable factors. The surfaces of samples were analysed by using SEM and AFM. Results indicated that the construction of the gas injection’ was the key parameter to suppress particle formation. Applying a multiple-hole injector at the back of the tube reduced these surface defects.