This study adopted observed Central Weather Bureau (CWB) hourly data from 1961 to 2011 in Taitung and Taichung. Foehn events were defined in terms of three major factors, high temperature, low relative humidity and strong wind speed. All the foehn events in Taitung and Taichung were divided into two types: events associated with typhoons (TYs) near Taiwan and independent events. The results of local winds based on the observational data are as follows. In both areas, the prevailing winds were mainly from the southwesterly direction, and the secondary winds were from the northerly to northeasterly directions. However, in Taichung, the northerly local winds of the foehn events related to adjacent TYs had a higher percentage to occur. This work used the European reanalysis (ERA)-Interim data of European Centre for Medium-Range Weather Forecasts (ECMWF) with high spatial resolution from 1979 to 2011. First, the rotated-extend empirical orthogonal function (REEOF) was applied by employing 850 hPa vorticity fields for 48 hours in each foehn case. Second, a composite analysis was applied for other variables (e.g. vertical velocity, winds) respect to the significant positive phases of the four major REEOF principal components in each type. From the composited circulation patterns, it can illustrate the time evolution characteristics for the foehn events associated with the four major REEOF modes for both types. Analytical results indicate that TYs and fronts are the main causes of foehn. As TYs were located around the Ryukyu Islands, or moved toward Nothern Taiwan (located around the Philippines or moved toward the Southern Taiwan), foehn events would occur in Taitung (Taichung) usually, sometimes in Taichung (Taitung). Otherwise, foehn could be also induced by southwesterly flow or northeasterly flow because of fronts. This investigation identifies crossing mountains, passing through valleys and splitting as the three main possible mechanisms to induce foehn when airflow interacts with terrain. As the wind flow is perpendicular to (parallel with) the mountains, mountain-crossing (valley-passing) subsidence may be the main mechanism. Furthermore, weaker winds tend to be split when they blow over Taiwan island. This may cause divergence in the windward side, which extends to strengthen the subsidence over the leeward side owing to the downslope winds. The three mechanisms may work together when the airflow crosses/passes the mountains, causing foehn in different time and space over Taiwan.