A fundamental problem with time series involves k nearest neighbor (k-NN) query processing. However, existing methods are not fast enough for large datasets. In this paper, we propose a novel approach, STS3, for processing k-NN queries that transforms time series into sets and measures the similarity under the Jaccard metric. Our approach is more accurate than Dynamic Time Warping (DTW) in some suitable scenarios and is faster than most existing methods, due to the efficiency of similarity search for sets. In addition, we developed indexing, pruning and approximation techniques to improve the k-NN querying procedure. As shown in the experimental results, these techniques could accelerate the query processing effectively.