According to the created robot theatre script, a big turtle robotic system was developed for performance at digital stage. This robot includes mechanics system and control system, and the mechanics system is composed of four 3-DOF modularized light weight legs a flexible neck with continuous curvature, a shell opening and closing device and a carbon fiber torso frame. All the mechanotronics devices, including motors, circuit board et al, are installed in the main body. Through the synchronous belt, the motion of the motor is transferred to the outer end, largely reducing the size and weight of the cantilever, then reducing the load of the motor. The control system consists of a PC and an embedded controller, respectively provides the functions of human-computer interaction at high level and the realtime control of each joint at low level. According to the requirement of performance at the stage, a COG self-adjusting gait planning method was presented, assuring the stability during the movement of multiple legs. Finally, the robotic prototype was developed which had beautiful appearance. After the verification based on certain experiments, the robot was used to conduct a number of public performances. The results showed that the developed robot perfectly played the role of the drama performance and provoked audience to love it.