In this paper, we address multiway network partitioning problem of dividing the cells of network into multiple blocks so as to minimize the number of nets interconnecting cells in different blocks while balancing the blocks' sizes. The sequential iterative improvement algorithm for the problem consists of several passes each of which is performed by repeatedly iterating the move operation. Therefore, the whole execution time taken by the algorithm is greatly affected by the number of the move operations and the execution time for each move operation. We present a fast parallel algorithm for solving the multiway network partiotioning problem by reducing both of them. We propose a new dynamic iterative method which reduces the number of move operations executed at each pass dynamically, and hence speed up the whole algorithm sharply. Moreover, we reduced the execution time of each move by its parallelization using the proper cell distribution.