The invention relates to a streaming time series data dimensionality reduction and simplified representation method based on piecewise linear representation. The method comprises the following steps that: S1: presetting data segments and compression parameters; S2: carrying out data scanning on streaming time series data in a slide window way, and entering a streaming data buffer zone; S3: judging whether the fitting error of an initial segmented data segment exceeds an ME_ES (Maximum Error for Entire Segment) or not, carrying out reservation if the fitting error of the initial segmented data segment exceeds the ME_ES, and marking the initial data segment as "inseparable", and if the fitting error of the initial segmented data segment does not exceed the ME_ES, carrying out secondary optimal segmentation; and S4: moving the data segment which is marked as "inseparable" in the streaming data buffer zone out of the streaming data buffer zone, judging whether the streaming time series data to be processed is in the presence or not, if the streaming time series data to be processed is in the presence, returning to the S2, and otherwise, ending. By use of the method, data dimensionality reduction execution efficiency is guaranteed to a high limit, the fitting accuracy of data simplified representation is optimized to a certain range, and accuracy and the execution efficiency of data representation can be improved.