This study is a part of an integrated project of real-time monitoring sea surface conditions around Taiwan coasts. Establishment of effective tidal simulations used to predict flow conditions around commercial harbors is the main objective of this part, in which comparisons of tidal flow simulation between Eastern and Western coasts of Taiwan will be presented here. Eastern coasts of Taiwan facing the Pacific Ocean is subjected to direct effect of tidal waves added with regular ocean current moving north. On the other hand, tidal waves entering the Taiwan Strait from both north and south openings change tidal characteristics to partial standing waves on the western coasts. It is interesting to see how to simulate tidal flows with different flow patterns mentioned above. Typical harbors, namely, Hualien and Taichung located on the two coasts are selected to demonstrate the results that include tidal analysis recorded at corresponding tidal station, selecting numerical computation domain and boundary conditions in numerical tidal model, verification of computational results, and interpretation of numerical results. Comparisons of tidal simulation on eastern and western coasts indicate that (1) selecting tidal analysis is important to provide basic information, (2) tidal direction and phase are critical to induce flow pattern, (3) tidal characteristics are different on both side of coasts. Represented flow patterns of high and low tides, and velocity flows fields will also be presented in the results.