Valve base electronics, connecting thyristor valve and DC control & protection equipment, is of importance to control and protect the thyristor valve. In the ±660 kV HVDC power transmission project, the thyristor valve and the control & protection system are supplied by different providers. In order to verify functions and performance of the interface between thyristor valve and control & protection equipment, the real-time close-loop simulation tests are carried out, where the overall situation is presented, the key technical problems and countermeasures are discussed, and the verification results are proposed. Close-loop tests of thyristor valve base electronics and control & protection system lay down solid foundation for on-site commissioning and successfully putting into operation of the project.