In digital substations， the hard-wired cables are replaced by the process bus for the transmission of AC signals， status signals and tripping signals based on the fiber-optic network. It is necessary to record and analyze the network communication process for the operation and maintenance of digital substations. An actual system is taken as an example to analyze the key techniques of the communication recorder and analyzer involving the communication on-line analysis and large amount of data storage. A specially designed smart network interface card（NIC） is used to enhance the network throughout and the amount of merging unit（MU） connected to the analyzer. The technical trend of network communication recorder and analyzer development is forecasted.