A method for detecting abnormal subsequences in data sequence includes constructing a hierarchical data structure of a target subsequence, each node in a bottommost layer of the data structure storing corresponding data of the target subsequence, and each node in a layer above the bottommost layer storing values based on data stored in corresponding nodes in a lower layer next to the layer above the bottommost layer; determining a second number of neighbors of the target subsequence based on the data structure of the target subsequence and of the first number of reference subsequences constructed in advance, the second number of neighbors having minimum Euclidean distances from the target subsequence; determining a third number of neighbors of each reference subsequence in the second number of reference subsequences, which have minimum Euclidean distances from each reference subsequence and determining whether the target subsequence is an abnormal subsequence.