The present patent application relates to a polarization interference optical interleaver, which includes a first port to transmit the first optical signal through the first optical path, a second port to transmit the second optical signal and a third port to transmit the third optical signal. The first optical signal passes through the first optical path and splits into the second optical signal and the third optical signal by the first and the second light splitting/combining crystals and the interference crystal group. The interference crystal group is located between the first and the second light splitting/combining crystals. The second optical signal and the third optical signal are received and reflected by a reflecting mirror. Then the second optical signal and the third optical signal output through the second port and the third port respectively. The second optical signal reflected by the reflecting mirror transmits along the first optical path of the first optical signal and passes through the interference crystal group, then walks off the first optical path by light walk-off device and outputs through the second port. The third optical signal reflected by the reflecting mirror transmits along the second optical path and passes through the interference crystal group, then outputs through the third port. There are only four beams in the interference crystal group of the present patent application. So the volume of the interference crystal group is minimized and the cost is reduced.