A dual-chip light splitting and light combining module is provided, which comprises a light splitting prism, a first mirror, a first polarizing TIR prism, a first displaying chip, a second mirror, a second TIR prism, a second displaying chip and a light combining prism. The dual-chip light splitting and light combining module is adapted to split an incident non-polarized light into a first polarized light and a second polarized light and combine the first polarized light and the second polarized light together. Also, a 3D projection optical system comprising the dual-chip light splitting and light combining module is provided.