Compared with software projects, the estimation of website projects is not mature enough without any methods for size or workload estimation. This paper researched Function Point Analysis (FPA), the most important size estimation method in software projects and then constructed Commerce Website Function Point Analysis (CWFPA) by introducing principles of FPA into commerce website projects. The paper reserved the basic definitions of software FPA for CWFPA and researched some key factors combined with characteristics of commerce website projects including the functional complexity, function point weight and value adjustment factor. In the end, a commerce website project PET was given as a demonstration of CWFPA.