In recent years, as Russia has increased its efforts on the exploration and exploitation of offshore oil and gas in the Arctic, relevant engineering technologies have attracted widespread attention. To reduce the exploitation costs, oil companies need a range of equipment for polar ice conditions. In this paper, design is carry out of the mooring system for a semi-submersible drilling platform designed for operations in polar seas. The water depth of this design is range 100m to 500m. The 1-year environment is selected as the design condition of operating mode, for survival mode, the 100-year environment is picked. To verify the positioning ability of the mooring system in polar sea environment, both weak ice and ice-free conditions are analyzed. Wind, wave, and current loads are selected as the main environmental loads in the non-glacial period, and, considering that waves are difficult to form and spread under ice conditions, wind, current, and ice loads are picked in the initial and final ice stage. The results show that if the harsh conditions such as icebergs are not considered, the conventional mooring chain can be used as the mooring system, which can meet the operation requirements of the platform in the summer and weak ice periods in the polar seas.