The invention discloses a closed-loop test system of a flexible direct current transmission system control and protection system. The closed-loop test system includes a real-time digital simulator, interface hardware equipment and control protection equipment of a modularized multi-electric level-based flexible direct current transmission device; the interface hardware equipment includes a power amplifier, a terminal type relay and a converter valve internal analog quantity and pulse expansion plate; the real-time digital simulator is connected with the control protection equipment of the modularized multi-electric level-based flexible direct current transmission device through the interface hardware equipment; and as a result, the closed-loop test system can be formed. The closed-loop test system is simple and flexible. With the closed-loop test system adopted, an entire modularized multi-electric level-based flexible direct current transmission actual control protection system can be tested conveniently and quickly.