The double crossover is usually adopted in terminal turnback of phased preliminary project. The turnback capacity and operational adaptability of the line would be restricted if the line stop extending. Hence, the technical route for studying the situation mentioned-above is proposed based on a case of Tanze Station of Phase 2 Project of Nanning Metro Line No. 2. And then the maximum turnback capacity of the double crossover is discussed in terms of driving and signal. Finally, the optimization measures, i. e. increasing the deceleration of train and laterally turnout crossing speed and line arrangement adjustment, are put forward, which can meet the short-term and long-term operational requirement and turnback capacity requirement.