The effect of CH4 flow rate on the structural and optical properties of boron-doped amorphous silicon carbon films as window p-layer in the industrial hydrogenated amorphous silicon solar module was investigated. The p-layer amorphous hydrogenated silicon carbon films were deposited from SiH4-CH4 gas mixtures in the Applied Materials SUNFAB radio frequency-plasma enhanced chemical vapor deposition Gen8.5 system with dimensions of 2.2 m 2.6 m. Infrared and transmittance/reflectance spectra were employed to analyze the bond configurations and optical properties of the films associating with structures of the p-layer films which are sensitive to the deposition condition. The optical band gap of the p-layer films increased as the CH4 flow rate ranged from 3000 sccm to 8850 sccm with other deposition conditions unchanged. With increasing CH4 flow rate, the deposition rate of p-layer amorphous silicon carbon films decreased slowly, because of the reduction of SiH3 radical in the SiH4-CH4 plasmas. The uniformity of the hydrogenated amorphous silicon carbon films was also investigated, by sampling and analyzing the deposition rate on four different locations of the large area films.