We investigate relaxation absorption of ultrasound and speed of sound dependence on temperature and constituent concentration of gas mixture.Two three-dimensional models,one based on molecular relaxation model and the other on sound velocity, are established for a sample consisting of carbon monoxide, nitrogen and oxygen.An algorithm is developed to reconstruct simultaneously temperature field,concentration field and flow of the mixture in sensing domain.Numerical simulation shows that the algorithm is feasible and applicable to measurement of complicated multi-physics fields.Errors arising in simulation are discussed.It is possible to use the algorithm for other component mixtures.