A portable optical detection chip comprises a substrate, a plurality of avalanche-type photosensitive device modules and a plurality of plane mirrors. The plurality of avalanche-type photosensitive device modules are formed on the substrate, and each of them comprises a plurality of avalanche-type photosensitive devices and a plurality of lenses. Each of the lenses is stacked on one of the avalanche-type photosensitive devices. The plurality of plane mirrors are disposed between the avalanche-type photosensitive device modules. That is, the avalanche-type photosensitive device modules are separated from each other by the plane mirrors.