A comprehensive steady-state population balance model is developed for the particle size distribution (PSD) of the polypropylene produced in tubular loop reactors. The model considers the flow type, the polymer particle dynamics, the particle growth and the attrition. Moreover, an empirical single particle model is used to describe the particle growth under internal and external heat and mass transfer limitations totally. The predicted PSD data obtained under steady-state polymerization conditions agree well with the actual data collected from industrial scale plant. The model are also used to predict the effects of some operational parameters on the polymer PSD produced under steady-state conditions. The results show that the polymer PSD are greatly affected by the feed catalyst size, the feed catalyst PSD, and the polymerization temperature. (C) 2008 Elsevier B.V. All rights reserved.