Upconversional fluorescence materials receive more and more attentions, but their applications suffer from the low conversional efficiency of fluorescence. In other words, it makes precise quantification difficult. In this study, a cube-corner retroreflector was introduced to collect more fluorescence from upconversional materials. A prototyping upconversional fluorescence detection system was developed with a dual optic path containing a cube-corner retroreflector and a coaxial multicore fiber for accepting fluorescence from both sides of the cube-corner retroreflector. A series of experiments were carried out to calibrate this prototyping system. It is found that the dual optic path can collect more fluorescence, and thus it improves the detection efficiency of weak fluorescence. The results confirm the feasibility of the upconversional fluorescence detection system with cube-corner retroreflector.