In the present study, we made efforts to realize a measurement method of instantaneous fluctuations of mass flux and concentration with 500 kHz bandwidth to explain supersonic mixing process. In our method, by using double-hot-wire probe which has two kinds of wires with different responses to the variations of mass flux and concentration, we were able to explain the mixing flow field with the help of calibration maps of each wire. Experiments were carried out in a 2D supersonic air/helium mixing layer at the Mach number of 2.4. The results show that the proposed method is very effective for the analysis of supersonic mixing. However, in selection of each hot wire, its diameter and thermal conductivity, both should be considered.