Dynamic monitoring and real-time decision-making system have high demand on the real-time property for wide-area measurements. Synchronization algorithm characteristics of phasor data concentrator and delay mechanism of wide-area communication network are analyzed， and a communication delay calculation model for wide area measurement system（WAMS） is proposed. The influence of SDH networks fault on real-time communication is studied. The two-fiber bidirectional multiplex section protection ring is used as an example to analyze the relationship between data loss and switching time length. The effect of increasing protection path delay on the overall communication delay of WAMS， and the corresponding countermeasures are given. The test results on practical system verify the correctness of the developed model. The research provides certain references for WAMS service network construction， optimized PMU configuration and PDC optimal placement.