The self-start procedure of the modular multilevel converter (MMC) based HVDC system which adopts clamp double submodules (CDSM) is analyzed. This procedure is divided into two basic stages, i.e., uncontrolled charging stage and controlled charging stage. The equivalent circuit in uncontrolled stage is simplified according to theorem of electrical circuit and the relationship between the maximum charging current and current-limit resistor is derived. Furthermore, it is indicated that all capacitors could not be fully charged to the rated value, owing to clamping functionality of diodes. In order to continuously charge these capacitors, three controlled charging methods are proposed, enabling that each achieves enough stored energy. Among them, method No. 1 takes advantage of the DC voltage controller, which uses the modulation and balancing strategy; method No. 2 and method No. 3 are realized by changing the charging loop’s equivalent electric potential and equivalent capacitance. In fully implementing the faults ride-through ability, auto-restart control sequences under temporary and permanent DC faults are designed. Finally, a digital model of the MMC-HVDC system with two active terminals is realized in the PSCAD/EMTDC software. The simulation results show that the proposed control strategies have satisfactory performance.