The invention provides a magnetic tunnel junction top electrode via forming method. The method comprises the following steps: S1, a substrate comprising a bottom electrode, a first dielectric layer, an MTJ structure unit and a tantalum top electrode is provided; S2, silicon nitride is adopted to fill the rest part of the substrate; S3, the silicon nitride is grinded until the tantalum top electrode; S4, a silicon oxide film layer, a top electrode via etching blocking layer and a second dielectric layer are deposited; S5, a top electrode via pattern is graphically transferred to the second dielectric layer; S6, the second dielectric layer is etched, organic matters left during the graphic transferring process are removed, and the pattern is transferred to the etching blocking layer; S7, the etching blocking layer is etched; S8, the silicon oxide layer is etched; S9, the left organic matters are removed; S10, a diffusion blocking layer is formed on the inner wall of the top electrode via; and S11, copper is adopted to fill the top electrode via, and a chemically mechanical polishing method is adopted to grind the filler.