A compact antenna array applied to 5G is designed, which is set approximately orthogonally by four antenna elements, and four half-wavelength microstrip lines are added to the upper and lower planes between the antenna elements to improve the isolation. The structure of the proposed antenna element and antenna array have been analyzed by high-frequency electromagnetic simulation software, and verified by experiments. The experimental results show that the operating frequency bands of the antenna array are 2.72-3.92 GHz and 4.74-5.42 GHz, respectively. The isolation between antenna elements is lower than -20 dB in the operating frequency band, covering two operating bands of 3.3-3.6 GHz and 4.8-5.0 GHz required for 5G completely. The antenna array is compact, only in the size of 68.5 mm× 68.5 mm×1.524 mm, which can be applied to 5G miniaturized portable devices.