Abstract: All the major magnets of a full superconducting Tokamak (FST) are superconducting magnets. The FST has higher running risk than other existing superconducting Tokamak. EAST (Experimental Advanced Superconducting Tokamak) is a FST. The interlock system & safety system (I&S) were developed for EAST to prevent human and devices from an accident. The supervisory safety interlock (SSI) system is the top level of the EAST I&S, which coordinates the secure running of all the sub-control systems. Based on the requirements of the EAST I&S, the SSI was developed with a programmable logic controller, interlock signal fiber optic network and optical-electrical converters. The SSI realizes events collecting, signals cycling scanning, protection action output, system status and faults log information recoding and real-time monitoring, etc. The actual mean scanning cycle value of the SSI is 0.7 ms, with maximum value about 3 ms, which meets the requirements of the EAST I&S.