The end-face reflection property of micro-nano fiber (MNF) is one of its important transmission features, which plays remarkable roles in a variety of practical applications of MNF. In this paper, we propose a novel method to study the MNF end-face reflection property using an optical circulator, which overcomes the deficiencies of the direct measurement relying on a 3 dB coupler. On the basis of this method, we further introduce the aerogel fixing and power compensation techniques to effectively eliminate the errors caused by MNF pigtail floating, the light source output instability and internal loss. Therefore, the whole experimental design improves the measurement accuracy. The MNF end-face reflections with respect to the diameter of MNF and the wavelength of the guided light are investigated. The experimental results are in good agreement with simulation results, showing that this new approach is reliable for measuring the reflectivity of specific MNF. This detailed investigation on the end-face reflection versus various factors will be conducive to the constructions of versatile micro-nano scale devices based on the MNF, such as the MNF lasers, MNF amplifiers, MNF couplers and MNF filters.