Abstract: Summer high temperature in Guangzhou is mainly caused by the dominance of the subtropical high and the peripheral subsidence airflow of typhoon systems. This paper uses a BDA (Bogus Data Assimilation) scheme to investigate the ability of the BDA scheme to improve the summer high temperature forecasting during the typhoon period. A high temperature event in Guangzhou in middle July 2005 is selected as a typical case of summer high temperature caused by both the subtropical high and typhoon (Haitang). We found from comparative analyses of the initial fields of a sensitivity experiment with and a control experiment without the BDA scheme that the scheme is able to adjust the location and intensity of the typhoon c enter and to make the model initial field more consistent with observations. It is also found that once better forecasts of typhoon track and its intensity change are obtained, the BDA scheme is able to improve the forecasts of summer high temperature and its distribution and the daily mean temperature of Guangzhou. Further, the mechanism leading to this difference is discussed. The strengthening of subsidence is the main reason that contributes to the improvement of temperature forecast. In the sensitivity experiment, the amount of moisture in the mid to lower troposphere above Guangzhou is reduced, and the air subsidence is strengthened. Therefore, the cloud amount in the sky is reduced and more shortwave radiation reaches the ground surface, which results in the rising of surface temp erature. Consequently more sensible heat fluxes are transferred to the surface layer and the surface air temperature rises. It is concluded that using the BDA scheme is able to improve the summer high temperature forecast in Guangzhou during the period of typhoon Haitang.