Digital PreDistortion (DPD) is a very useful method to improve the linearity of Power Amplifiers (PAs) for LTE and upcoming 5G networks. As the spectrum resources are becoming more and more crowded, and the communications bandwidth are broader, the ACPR (Adjacent Channel Leakage Ratio) is very important to communication systems. DPD is one of the useful means for PA to reduce ACPR. This article demonstrates what DPD is and how DPD is achieved, the measurement of the Digital Distortion of a PA using a vector generator and vector analyzer, and the measurement results has been discussed.