The design and development of composite materials with novel structures is one of the effective ways to enhance the electrochemical properties of supercapacitors. In this paper, a one-step electrodeposition method is used to adjust the morphology and structure of CoMnS nanomaterials by changing the amount of CS₂. CoMnS nanomaterials with unique flower-like structures are reasonably prepared, which promotes the flow of electron transfer and improves the electrochemical behavior. It is worth noting that when the amount of CS₂ is 4 mmol, the specific capacitance of CoMnS-4 reaches 3469.5 F g⁻¹ at 1 A g⁻¹, and the specific capacitance is still 2830.5 F g⁻¹ (maintaining 81.56%) until the high current density reaches 20 A g⁻¹. After 10 000 cycles, it shows excellent cycle stability (maintaining 95.78% at 20 A g⁻¹). The CoMnS-4//AC asymmetric supercapacitor device has an excellent energy density of 85.91 W h kg⁻¹ when the power density is 800 W kg⁻¹, which shows it's great application value.