A closed-track optical delay module, a terahertz system, and a photoelectric system are provided. The closed-track optical delay module comprises a first constraint component with a closed-track line structure, a second constraint component with a straight line groove, a third constraint component with a positioning convex, a light conversion device, a housing, and a driving control device. The positioning convex forms a constraint fit relationship with the closed curve groove and straight line groove. One of the first, second, and third constraint components is connected with the driving control device, the other is fixedly disposed, a next one is connected with the light conversion device and moves parallel to the straight line groove. A light input interface is used for an incident light to be irradiated onto the light conversion device. A light output interface is used for a delayed beam to be emitted from the housing.