In the RoboMaster competition, traditional uncontrolled dart systems using friction wheels have problems such as low launch accuracy and a lack of guidance capabilities, resulting in a low hit rate. To solve these problems, this paper designs and implements a guided flight dart system based on proportional navigation. Regarding the mechanical design, the launch module of the dart launcher uses a rubber-band ejection instead of a friction wheel, which improves launch accuracy and reduces overload. The attitude adjustment module selects a variable-length triangular bracket configuration to improve launch stability. The loading module adopts an umbrella-shaped structure that can carry 3 darts. The dart itself uses a conventional aerodynamic layout and achieves static stability through a reasonable layout of internal devices. In terms of the guidance algorithm, we establish the aerodynamic model of the dart and verify its static stability. An improved 3D proportional navigation law is used to reduce the jump in required normal overload at the terminal phase. Simulation tests show that the miss distances of this system when hitting the outpost and the base are 0.013 m and 0.034 m respectively. In the physical test, each module of the launcher has stable and great performance. This research provides a high precision guided dart solution for the RoboMaster competition.