Executing business workflows on large-scale heterogeneous distributed computing systems is a challenging task. The grid workflow is aimed at enabling resource sharing and coordinated problem-solving between computers and people in a distributed and heterogeneous manner. In this paper, we present a formal specification methodology for grid workflow modeling which is founded upon the Pi-calculus and CTR technology. This method works well for characterizing the behaviors and interactions of the workflow processes that belong to grid environment in terms of the semantics of pi-calculus and CTR methodology. Experimental results show that the proposed method can be used for grid workflow execution and can effectively execution of grid processes automatically.