The contradictions between multi-objectives are prominent under the regulation of cascade reservoirs. In order to realize the synergy and equilibrium of different benefits, firstly, the primary and secondary benefits of multi-objectives are identified, and a multi-objective synergistic regulation model for reservoirs is established based on synergetics theory; secondly, a method of multi-objective balanced benefit regulation is proposed based on satisfaction boundaries; lastly, the correlation dimension of the chaos theory and Kolmogorov entropy are used to identify and guide the chaotic characteristics of multi-objective regulation system of cascade reservoirs. The application results in the upper Yellow River cascade reservoirs show that under the proposed theory and method, the benefits of multi-objectives can reach a satisfactory state of synergy and equilibrium within a certain period of time without reducing the guarantee level of multi-objective benefits. The synergistic degree of the multi-objective regulation system in the final scheme is 0.64, and the guarantee degree of the primary benefits of multi-objectives are higher than the secondary benefits. This study provides a new approach for the efficient utilization of water resources in water-deficient basins afflicted by competitions between multi-objectives, expands the research scope of multi-objective optimal regulation of reservoirs, and promotes the intersection and fusion of system engineering, synergy and chaos in the field of water resources research.