In view of strong nonlinearity and uncertainty of VSC-MTDC systems, a novel sliding-mode current control strategy based on exponential reaching law is proposed. The inner loop current proportional integral (PI) control is replaced by a sliding mode current control when the direct current control is used in HVDC converter stations, which reduces a PI controller compared to traditional double loop PI control and simplifies the parameter adjustment process of the system. A sliding-mode variable structure controller is established in which the errors of the d-axis current and q-axis current in inner loop are selected as a hyperplane in the rotating coordinate system, and the global stability of the control system is analyzed via Lyapunov function, the fast adjustment of power can be ensured when the converter station switches off because of fault, the stability of DC voltage can be maintained when the equivalent impedance of AC system changes. Finally, a multi-terminal HVDC transmission system connected to large offshore wind farms is built in PSCAD/EMTDC, the proposed control strategy is compared with traditional PI control strategy, and simulation results indicate that the proposed control strategy possesses good dynamic and steady state performances.