Increasingly more organizations are involved in critical cross-organizational business processes. Reachability analysis is one important way to guarantee the correctness of these processes. This paper proposes a new way of combing Role Network Model (RNM) and Picalculus to support reachability analysis for distributed and highly dyanmic processes. We first formally describe RNM in Pi-calculus. We then propose a reachability verification method based on RNM and μ-calculus for both structured and dynamic business processes. We evaluated our approach using a real-world government administrative permit system in China. The results show that proposed method can analyze and improve the reachability aspects of cross-organizational business processes, especially for dynamic business processes. 