Given a directed bipartite graph with a node set , and an arc set , where , , and . Chen (1995) presented an time algorithm to solve the parametric bipartite maximum flow problem. In this paper, we assume all arcs in have infinite capacity [such a graph is called closure graph Hochbaum (1998)], and present a new approach to solve the problem, which runs in time using Gallo et al's parametric maximum flow algorithm, see Gallo et al. (1989). In unbalanced bipartite graphs, we have , so, our algorithm improves Chens's algorithm in unbalanced and closure bipartite graphs.