Embodiments of the invention provide a substrate etching method, which includes: a deposition operation for depositing a polymer on a side wall of a silicon groove, an etching operation for etching the side wall of the silicon groove, and repeating the deposition operation and the etching operation at least twice. In the process of completing all cycles of the etching operation, a chamber pressure of a reaction chamber is decreased from a preset highest pressure to a preset lowest pressure according to a preset rule. The substrate etching method, according to various embodiments of the invention, avoid the problem of damaging the side wall, thereby making the side wall smooth.