Start-up control is an important additional control in the system of multi-terminal HVDC based on voltage source converter (VSC-MTDC). Appropriate startup control can reduce the impact of over-voltages and over-currents on the AC grid, and avoid the damage to equipment. To this end, the analysis of the over-voltage and over-current causes has been done; and then a start-up control strategy which is suitable for the VSC-MTDC system has been designed; at last a VSC-MTDC system model has been built in the software PSCAD / EMTDC to verify the effectiveness of the procedure. Simulation results show that the control strategy can effectively restrict the over-voltage and over-current in the start-up process, which ensures the system’s smooth transition to its rated state.