Typhoon Morakot (0908) caused severe damage. In order to explore the underlying reasons, the phenomenon that the intensity of the typhoon always remained around 960 hPa and did not reduce when it passed over the island of Taiwan is studied from both observational and numerical simulation results, by using the NCEP/NCAR1°×1°data and WRF numerical model. The observational analysis shows that the no reduction of Typhoon Morakot’s intensity was closely related to the interaction between Morakot and Goni (0907), which was in its southwest direction, and some physical quantities from Typhoon Goni were continuously transported into Morakot, such as the inputting of water vapor were mainly from 950 to 850 hPa, but rarely above 600 hPa. The transmission of vertical velocity existed in the whole layer, extending from 1000 hPa to 300 hPa. The positive vorticity (negative divergence) was transferred at the lower levels, and the negative vorticity (positive divergence) at the upper levels. Using the WRF numerical model for each control and sensitivity experiment in which Typhoon Goni was filtered, the results show that vorticity, moisture flux, divergence, and other physical quantities from Typhoon Goni were transported and involved in Typhoon Morakot, and thus they gave positive contribution to the maintenance and no reduction of Typhoon Morakot intensity when it passed over the island of Taiwan.