This article explores a method of optical transmission inspection of the basis weight on-line, by combining the modified least squares and optical processing technique. This process is developed to significantly target toward improving the mass quality analysis of the nonwoven material. The real-time scanning width piecewise least squares method and area-based strategy for determining based on the process quality of nonwoven manufacturing. To avoid the influence of ambient factors, the compensation controls device are adopted and successfully showed. Subsequently, the modified least squares method is used to obtain the suitable parameter transformation between the measured voltage and the nonwoven fabrics basis weight. The piecewise least squares method was obtained as the parameter transfer equation. We consider estimating and testing C pk with the presence of on-line basis weight measurement errors. To obtain the true process precision C p and integrated process capability index C pk are presented to practitioners for their factory applications.