A method for packaging the sensor units is shown below. First step is providing a substrate, and each sensor area on the substrate is partitioned into two individual circuit areas. An emitter and a detector are installed on the two circuit areas respectively. Step two is forming a first packaging structure to cover the two circuit areas, the emitter and the detector by a mold. Next step is cutting the first packaging structure to form cut groove between and around the emitter and the detector. Next step is forming a second packaging structure in the cut grooves by the same mold. At last, the panel of sensor units is diced and separated as individual sensor units. As above-mentioned, the second packaging structure is used for isolating the signals of the emitter and the detector.