In the actual power system, the load changes at all times under the influence of various factors and it can be regarded as a continuous function. The development of smart grid makes continuous time data acquisition and generator control come true, so the continuous time load dispatching is imminent. However, the economy and security of the original static and dynamic optimal power flow are limited to some extent with considering the optimization of discrete functions. The Riemann integral method is applied to expand the optimal power flow, which consider continue time change of variables. A continuation optimal power flow model is established based on Riemann integral. The precision and efficiency of the algorithm is verified through the stimulation of IEEE 5-bus system. Simulation results show that a final optimal dispatching is found in the proposed model with all the chance constraints satisfied. Moreover, the active power outputs of generators flow the fluctuation of load well.