The invention relates to polydopamine modified magnetic balls, a synthetic method of nanomaterial by fixing Ti<4+> on the surfaces and an application thereof. The synthetic method comprises the following steps: dispersing magnetic balls in a 
dopamine-contained water solution, quickly adding a trismetyl aminomethane 
buffer solution in the 
dopamine-contained water solution in which the magnetic balls are uniformly dispersed under the mechanical stirring condition, mechanically stirring for 10 to 16 hours at a 
room temperature, and washing and carrying out the 
magnetic separation to obtain nanomaterial which is good in dispersivity in the water and provided with the polydopamine modified magnetic balls on the surfaces, and dispersing the material in a 100 mmol / L Ti(SO4)2 solution, mechanically stirring for 2 to 3 hours at the 
room temperature, and washing and carrying out the 
magnetic separation to obtain polydopamine modified magnetic balls, and nanomaterial by fixing Ti<4+> on the surfaces of the magnetic balls.. The method for fixing Ti<4+> is very simple, a layer of polydopamine is modified on the surface, so that the material has excellent 
environmental stability and 
biocompatibility, and is good in dispersivity in the water, and the material can fix a large amount of Ti<4+>, and takes the magnetic balls as a core to cause the material to be simple to operate and carry out 
magnetic separation, the synthetic method is simple, and low in cost, and can enrich 
phosphorylated peptide by a high-flux MALDI-TOFMS.