In this paper, a practical qualitative +quantitative method named S-ANN is proposed as a forecasting tool, in which the artificial neural network (ANN) of AI is used to handle the quantitative knowledge and the SCENARIO method of systems engineering is used to handle the qualitative knowledge respectively. As a case study, S-ANN method is employed to forecast the ridership of Beijing public transportation, the results show that S-ANN method possesses advantages of feasibility and easily to operate.