Based on the intra-annual and inter-annual change characteristics of the river flow process, this paper put forward a probabilityweighted FDC(flow-duration curve) method to calculate the stream basic ecological flow for the typically wet, normal and dry years. The probability is based on the historical data with the Copula function method. The approach was tested in the Jinshajiang River and the resultswere evaluated by the Tennant standard and compared with month-by-month minimum ecological runoff method, dynamic calculation method and modified FDC method. The results show that the stream ecological demand can be perfectly met. Besides, this approach isreasonable and reliable under the proof of experimental data.