The correctness of operation of power dispatcher has an important impact on the safe and reliable operation of power grid, which is closely related to non-real-time factors such as dispatcher's work experience, sense of responsibility and historical operational accuracy, as well as real-time factors such as dispatcher's working hours, on-duty shifts and psychological state. This paper models the human factors influencing the accuracy of dispatching operation, takes the reasonable distribution of workload of different shifts into account, aims at minimizing the total human risk, and uses bacterial colony chemotaxis algorithm to optimize the allocation of daily power grid dispatching tasks. Taking the actual dispatching tasks of a certain power network as an analyzing example, the allocation result ensures that the workload of each shift is balanced while the total human risk value is minimized, which verifies the effectiveness of the proposed model and method. This work is supported by National Natural Science Foundation of China (No. 51767002).