Abstract: With the increasing penetration of volatile renewables, more power regulation capacity is needed for the power system. To determine sufficient and reasonable regulation reserve, the coordination between economic dispatch and Automatic Generation Control (AGC) is indispensable. This paper proposes a discrete-continuous-time stochastic look-ahead economic dispatch model considering the dynamic characteristics of AGC provided by regulating resources, so as to make scheduling decisions that balance the energy balance and regulation requirements, achieve the optimal allocation of fast and slow resources, and enhance the dynamic regulation ability of the system. In the propose model, a discrete-time model is established to precisely characterize the dynamic characteristics of AGC regulating resources for current time period, and an approximated continuous-time model is used to formulate the AGC resources' characteristics for the look-ahead time period to reduce the complexity of the overall model. To further make the problem tractable, the charge and discharge complementary constraints of energy storage is relaxed by introducing appropriate penalty term in the objective function. Finally, the benders decomposition algorithm is adopted to solve the problem in parallel manner. The numerical tests are conducted in PJM 5-bus system and IEEE 118-bus system. The results show that the proposed model can effectively reduce the system frequency deviation compared with the traditional model. Compared with the model considering refined AGC dynamic constraints in the look-ahead period, the computation burden of proposed model is significantly reduced.