In 0.476 m diameter flat bottom stirred tank,single-impeller of improved 6-BT (6-BT fin-type)and ordinary 6-BT type were used,respectively.A pressure transducer was proposed for detecting the Macro-Instabilities(MIs) that can take place inside a stirred tank.The experimental technique and the time series analysis method, based on wavelet denoising and Fast Fourier Transform (FFT) were shown to provide reliable information on the frequency of MIs.Results showed that compared to the ordinary type impeller, the MIs of fin-type impeller was larger with the same rotational speed, and it also enhanced the mixing performance.