Based on the actual experiment signal of draft tube in Huangbizhuang unit, the time domain site nal h as been carried on the spectral analysis; embeddirg dimension and the correlation dimension also have been analyzed in different conditions of draft tube. Results show that when the embedding dimension is greater than or equal to 18, correlation dimension is tending to stability, so the minimum embedding di- mension is 18. And when the guide vane opening(a) is 50.70% and 62.85%，the correlation dimension 3. 4566 and 3. 3881 respectively. This can be ohtained that under different working conditions, correlation dimension is different, accordingly, the correlation dimension can be used as a conduit for pressure pulsa- tion of draft tube, and it can guide the stable operation of the power.