In order to accurately understand the coordinated evolution patterns of the cascaded reservoir system in the Yellow River Basin, based on synergetics theory, order parameters of flood-sediment transport, ecological environment, and socioeconomic subsystems in different reaches of the Yellow River Basin were identified. The variation characteristics of these order parameters were analyzed, and the evolution characteristics of coordination degree of the cascaded reservoir system from 1965 to 2020 were clarified. The results show that, from 1965 to 1985, the multi-year average runoff of the basin was relatively abundant. Although the water consumption in the basin gradually increased, the overall system remained in a self-balanced and well-coordinated state. However, due to the limited regulation capacity of reservoirs, order parameters were largely affected by natural runoff and sediment conditions, resulting in large interannual fluctuations in system coordination degree. In the middle reach, the cascaded reservoir system even dropped to a moderately uncoordinated state in some years. From 1986 to 2001, due to the operation of the Longyangxia Reservoir, the immaturity of the unified dispatching system, and the rapid increase in water consumption in the basin, order parameters were adversely affected. The system’s balance was disrupted, leading to a degline to a barely coordinated state. The lower reach experienced the sharpest decline in the system coordination degree, even reaching a severely uncoordinated state in some years. From 2002 to 2020, the cascaded reservoir regulation system was improved, the water allocation in the basin became more reasonable, and order parameters were recovered. Then, the system entered a new coordinated stage, rising to a primary coordinated state and showing an upward evolutionary trend.