The approximation of overall aerosol extinction coefficient is conventionally achieved through integrating the single particle extinction efficiency over the whole size distribution, which consumes much computational time. In this work, a new approximated scheme with higher efficiency relative to the conventional scheme is proposed, in which the combination of polynomials for fitting Mie’s solution and the method of moments is to produce the overall extinction coefficient of an evolving nanoparticles. The closure of arbitrary moments is achieved by implementing the Taylor-series expansion method of moments. The new approximated scheme was verified by comparing it to a more exact referenced scheme under two different typical aerosol modes, namely nucleation mode and accumulation mode. The study verified the new scheme is a reliable method for approximating overall extinction coefficient during aerosol evolution with acceptable efficiency and accuracy, thus it is suitable to be used in some atmospheric aerosol models.