In this paper，we disclose the relations between multi-relaxation absorption and the acoustic parameters when ultrasound propagates in gas mixtures，such as the relation between concentrations of constituents and acoustic frequencies. In the meantime，the dependence of acoustic velocity on the same parameters is discussed. Based on the sample consisting of carbon monoxide，water vapor，nitrogen and oxygen，we establish the three dimensional model for the relation between concentrations of mixture constituents and relaxation absorption and acoustic velocity，respectively. Further more，we give the two dimensional dependence between relaxation absorption and acoustic frequency. We propose a simplified algorithm to calculate the carbon monoxide concentration by measuring the relaxation absorption and acoustic velocity. Simulation results proved the feasibility of this method and showed the appropriate range of acoustic frequency. The origins of errors arising in the application of the method are indicated in this paper.