In this paper, a dual-polarization antenna based on substrate integrated suspended line (SISL) technology and applied for the 5G millimeter-wave band is proposed. This antenna consists of five dielectric substrates and ten metal layers. By adding stacked parasitic patches, the antenna expands its impedance bandwidth to 26.30-29.61 GHz, covering the N257 band in 5G mm-wave communications. The impedance bandwidth of the proposed antenna has increased by 8.15% after adding the stacked patch. This antenna also uses the “T”-type coplanar coupling feed method and differential feed structure to enhance port isolation. The port isolation degree of the antenna in the working band is less than −55 dB, the cross-polarization ratio is less than 50 dBi, and the gain is from 6.27 to 7.96 dBi.