The invention provides a manufacturing method of a T-shaped gate of a transistor with high electron mobility. The manufacturing method comprises the following steps: S1, growing a Si3N4 dielectric passivation layer on the surface of the transistor; S2, uniformly coating the dielectric passivation layer with high-light-sensation positive photoresist for baking; S3, exposing and developing the high-light-sensation positive photoresist in a stepping exposure way to form a gate groove etching window, and carrying out baking; S4, etching the dielectric passivation layer to form a gate groove, and removing the high-light-sensation positive photoresist; S5, uniformly coating the surface of the transistor with negative photoresist, and photoetching the negative photoresist to form a gate cap line; S6, evaporating a gate metal, and carrying out stripping to obtain a gate electrode. By the adoption of a stepping exposure and photoresist shrinkage process and ICP-RIE etching for adjustment of the feature size of a target line, a gate line with the feature size of 0.1 to 0.5 [mu]m can be flexibly manufactured; compared with an electron beam exposure mode, the manufacturing method has the advantage that the production efficiency is greatly improved, and is applicable to batch production.