Abstract: The uncertainty of network delay is the technical difficulties in network sampling and trip scheme for smart substation. But the protection device can restore occurrence time of received sampling data at multiple intervals through merging unit inherent delay and the total delay ΔT of spaced link resides calculated by delay controllable switcher, then synchronized sampling is implemented. In order to verify the preciseness of time delay algorithm, transmission accuracy and reliability of delay controllable switcher, a network test system is built to compensate time delay, to precisely control data flow, to deal with such functions as protection device, and to testify and analyze its performance and reliability. In the end, the recommended network scheme and main requirements of technical index are put forward.