Abstract: The heave motion of semi-submersible drilling platforms is a limiting factor for drilling operations. In this paper, a semi-submersible platform in South China Sea is installed with an active heave plate, which is designed on the principle of turned mass dampers. In order to reduce the heave response of the platform, the hydrodynamic parameters of the platform is computed in a frequency domain by AQWA software, and the time domain model of this new type of platform is built in Simulink. According to the principle of minimizing the heave motion under the sea state of work in South China Sea, the stiffness and damping ratio of the conjunction is optimized; the heave performance of this new type of semi-submersible platforms is conducted, which is compared with traditional semi-submersible platforms and semi-submersible platforms with fixed heave plates. The results indicate the installation of an active heave plate can reduce the heave response of the semi-submersible platform under normal sea states more effectively, providing a new way to control the heave motion of semi-submersible platforms.