The invention discloses a formation method of a 3D magnetic sensor. The method comprises steps of providing a substrate, forming an insulating layer and a groove positioned in the insulating layer on the substrate, forming a magnetic material layer, ensuring that the magnetic material layer covers the insulating layer and the bottom and side walls of the groove, forming a TaN layer on the magnetic material layer, forming an etching blocking layer on the TaN layer, forming a filling material layer on the etching blocking layer, ensuring that the filling material layer is filled in the groove, forming a graphical photoresist layer on the filling material layer, taking the graphical photoresist layer as a mask, etching the filling material layer through plasma, taking the graphical photoresist layer as a mask to etch the etching blocking layer and the TaN layer, removing the graphical photoresist layer and the surplus filling material layer, and etching the magnetic material layer to form a magnetic resistance layer before or after the graphical photoresist layer and the surplus filling material layer are removed. The etching blocking layer blocks the plasma bombardment on the TaN layer during the process that the filling material layer is etched, so that good performances of the 3D magnetic sensor are guaranteed.