A support assembly includes a left support frame, a right support frame, and a bracket. The left support frame and the right support frame are both slidably connected to the bracket. The bracket defines receiving grooves. The left support frame includes a first tooth portion. The right support frame includes a second tooth portion. When the support assembly is in a folded state, teeth of the first tooth portion and teeth of the second tooth portion are received in the receiving grooves to support the screen assembly in a retracted state; when the support assembly is in an unfolded state, the teeth of the first tooth portion and the teeth of the second tooth portion extend out of the receiving grooves to support the screen assembly in an extension state. A dial plate and a smart bracelet are further provided.