In the research domain of time series similarity, there have been many approach that are developed to represent time series in the order of reducing the dimensionality. As one of the classic time domain-frequency domain transformation method, the discrete cosine transform has been widely used in the field of graphics and image processing. In this paper, we used this method to represent time series, and implenmet querying operation etc. on the transformed data. Our experiments indicate that this method obviously improve the performance compared with previous method.