A trench MOS structure is provided. The trench MOS structure includes a substrate, an epitaxial layer, a trench, a gate isolation, a trench gate, a guard ring and a reinforcement structure within the guard ring. The substrate has a first conductivity type, a first side and a second side opposite to the first side. The epitaxial layer has the first conductivity type and is disposed on the first side. The trench is disposed in the epitaxial layer. The gate isolation covers the inner wall of the trench. The trench gate is disposed in the trench and has the first conductivity type. The guard ring has a second conductivity type and is disposed within the epitaxial layer. The reinforcement structure has an electrically insulating material and is disposed within the guard ring.