摘要：We designed a new tuning system for SFC D circuit. It is a device to carry out auto tuning.D circuit consists of cavity and D-model box, it is an important part of accelerator. When accelerator works it can be fed power and to have ion accelerated. D circuit sketch map and frequency tuning system are shown in Fig.1. There is much factor effect so D circuit parameter is not stable (include mechanical tremble and metals expand with heat). We need frequency auto tuning system of D circuit that can realize frequency stability.