A trench gate manufacturing method includes the following steps: Step 1, forming a trench in the surface of a semiconductor substrate; Step 2, forming a first oxide layer; Step 3, selecting a coating according to the depth-to-width ratio of the trench and forming the coating completely filling the trench; Step 4, etching back the coating through a dry etching process; Step 5, conducting wet etching on the first oxide layer with the coating reserved at the bottom of the trench as a mask so as to form a gate bottom oxide; Step 6, removing the coating; and Step 7, growing a gate oxide. By adoption of the trench gate manufacturing method, a BTO can be realized at a low cost, and can be well-formed in trenches with smaller depth-to-width ratios and thus is suitable for forming BTOs in trenches with various depth-to-width ratios, thereby having a wider application range.