Protein phosphorylation is one of the most important post-translational modifications in mammalian.Large scale identification of phosphoproteins and phosphorylation sites are highly beneficial to understand the functional mechanisms of protein phosphorylation.However, identification of protein phosphorylation still remains challenging because of the low abundance of phosphoproteins and large interference from non-phosphorylated signal.Therefore, it is necessary to enrich phosphoproteins or phosphopeptides before analysis by mass spectrometry.