A plastic light-folding element includes an incident surface, an exit surface, at least one reflective surface, at least one connecting surface and at least one gate vestige structure. The incident surface is configured to lead an imaging light enter the plastic light-folding element. The exit surface is configured to lead the imaging light exit the plastic light-folding element. The reflective surface is configured to fold the imaging light. The connecting surface is connected to the incident surface, the exit surface and the reflective surface. The gate vestige structure is disposed on the connecting surface. At least one of the incident surface, the exit surface and the reflective surface includes an optical portion and an arc step structure, the arc step structure is disposed on a periphery of the optical portion, and an arc is formed by the arc step structure centered on the optical portion.