A transmission line model capable of predicting the reflection phase of high impedance surfaces in normal incident is proposed. The surface impedance of high impedance surface （HIS） can be regarded as the effective capacitive impedance of patch array in parallel with the inductive impedance of substrate layer, and the effect of vias conductor can be ignored at normal incidence. Results of the a nalytical model agree well with the HFSS simulated results. HIS with different parameters are fabricated and tested, the reflection phase of HIS predicted using the transmission line model agree well with the measured results, which proves the validity of this transmission line model.