In order to distinguish trends and abrupt changes in hydrological time series, the generalized LASSO model based on L₁-norm regularization was used to detect changes in hydrological series. It is found that the annual mean streamflow series at the Cuntan Station shows a downward step change in 1969. Furthermore, trend analysis shows that both the sub-series before/after 1969 and the whole series after removing step change components show no significant trend, indicating that the assumption of the step change in the annual mean streamflow series at the Cuntan Station is reasonable. The conclusions obtained from the generalized LASSO method are consistent with those obtained from other change detection methods.