Due to the uncertainty of SV packet transmission delay in the switches,the sampling synchronization is mainly achieved by unified synchronous clock connected to merging units of the whole smart substation at present,resulting in network synchronization heavily dependent on the external clock.It also violates the basic principle of protections not relying on external time synchronization system.Sampling synchronization technology is the key point of true actual application of “network sampling” method and the network structure of smart substation can be greatly simplified if the sampling synchronization problem is well solved.This paper gives a detailed analysis of the advantages and disadvantages of various sampling methods,and puts forward a new type of synchronous sampling principle based on delay measurement of switch data transmission,which is simple and reliable.The correctness check of delay measurement of the switches can be achieved by evaluating the rationality of the equivalent merging unit data receiving time.This scheme has very good promotion prospects.