Many enrichment techniques for phosphopeptides usually rely on the interaction of phosphate groups with metal ions or metal oxides. Based on this, we innovatively designed and fabricated an electrochemical sensor based on TiO2 nanoparticles (NPs), which can sensitively and rapidly detect phosphopeptides in protein samples pretreated with AuNPs. When the phosphopeptide solution was pretreated with AuNPs, AuNPs can be linked to the polypeptide chain via the amino group at the tail of the polypeptide chain. When TiO2 NPs are specifically bound to the phosphate group on the peptide, the modified AuNPs can improve the electron conduction ability of the electrode to detect the phosphopeptides. The designed electrochemical sensor had the advantages of high sensitivity, selectivity, and repeatability, and it showed a wide linear concentration range (1 pg/L to 1 mg/L) and a lower limit of detection (0.24 pg/L) for phosphopeptides. In order to improve the detection capability of the electrochemical sensor, we also synthesized TiO2 and graphene oxide (GO) composite materials. The influence of the morphology and crystal form of TiO2 NPs on phosphopeptide detection was studied by changing the feeding ratio and heat treatment temperature. We found that the uniformly dispersed anatase crystal TiO2 and GO composite-modified electrode showed a lower detection limit (0.37 ag/L). This sensing strategy is expected to provide a novel solution for the direct detection of phosphate groups in polypeptides in complex environments.