Controllable line-commutated converter (CLCC) topology realizes reliable recovery of main branch thyristor and controllable shutdown of bridge arm by adopting hybrid structure composed by thyristor and IGBT devices, in combination, solving the commutation failure problem of conventional DC converter fundamentally. In this paper, the design and prototype development of CLCC valve are described in detail from four aspects: electrical design, structure design, valve control design and test verification. Firstly, the collaborative design method of series number, damping capacitance and arrester parameters of fully controlled sub-valve and thyristor sub-valve is described. Taking Nanqiao Station of ±500kV/1200A Genan Project as an example, the electrical parameters design of ±500kV/1200A CLCC converter valve is carried out. A compact modular valve tower with the main and auxiliary branches suspended in separate columns and digital - analog hybrid valve control system is developed. Finally, the controllable turn-off test is carried out on the valve module. Test results show that the CLCC converter valve can actively turn off the maximum fault current and realize the reliable turn-off of thyristor, which verifies the ability of resisting commutation failure and the feasibility of engineering application.