Abstract: Based on comprehensive data including radiosonde observations, FY-2C satellite images, products from CIMSS, Best Track Data of CMA, NCEP reanalysis data, outputs from models of ECMWF, JMA, CMA (T639), and STI (SHTM-Shanghai Typhoon Model, Shanghai Ty-phoon Institute), an analysis on environment systems transition and verification of numerical model products are performed to probe the turning cause and forecast error of super typhoon Muifa. Some facts are revealed as follows: the subtropical high located on Japan extends south-ward and is connected with a weak anticyclone southeast to Muifa, resulting in an intensification of the southerly steering flow of Muifa, which acts as a significant role in the turning of Muifa during 4th-5th Aug. 2011. Forecast analysis illustrates that real-time correction processes are necessary for prediction products by numerical models according to actual weather situation before using. A multi-area searching could be a better method for finding similar typhoon track according to the historical storms.