To identify pollen sources that influence to the urban area is the one of most important issue for the countermeasure to pollen forests. In this study, focused on the 2005 pollen dispersion season in Japan, we discussed the method how to identify the source forests of pollen that provides pollen to Tokyo Metropolitan area. On Laglangian numerical forecasting model for Japanese cedar pollen dispersion, we add source information to each particle and count the number of particles arrived at Tokyo by using the marker respectively added. By evaluating the impact ratio of each forest, large impact pollen source forests to the urban area were identified.