Abstract: The paper indicated it not only has low efficiency of data mining to directly use original gas concentration time series to forecast short-term concentration,query similarity and classify and cluster time series,but also affects accuracy and reliability of data mining of time series.It put forward a pattern representation method of gas concentration time series based on piecewise linear method.By use of the piecewise linear method to make pattern representation of gas concentration time series,gas data storage and cost of count are smaller,only main form of gas concentration time series is reserved,and detailed interferes are went out,so the results of pattern nopresentation can reflect itself characteristics of gas concentration time series and and the method is good for improving efficiency and accuracy of data mining.