Usually, freeform optical surfaces do not have rotational symmetry compared with traditional spherical and aspheric elements, so they have more freedom for system design. In some optical systems which have strict package requirements, such as overall length, weight and volume etc., freeform optical elements can help to satisfy these requirements through reducing lens number of the system. In this paper, the design method of freeform optical elements was introduced, and proposed several design examples of the optical system were proposed which adopted freeform optical elements. From these design examples, the advantages of using freeform optical elements could be proved. The size of the microdisplay used is 0.61 inch and FOV is 45°. The exit pupil diameter is 10 mm.