The invention discloses an alternate iterative algorithm for temperature field and concentration field reconstruction based on spectral absorption. First, a linearization scheme is provided for calculation of a concentration field, an original system is semi-linearized, and thus the nonlinearity of the original system is weakened; then, an alternate iteration scheme is provided for the temperature field and the concentration field to be measured, and a half of the number of unknown variables is reduced in each iteration; finally, a penalty term is introduced through an optimization technology to overcome the morbidity in the reconstruction process, regularization parameters can be adjusted automatically in each iteration, and it is guaranteed that an iterative solution converges to an exact solution. According to the alternate iterative scheme, on the premise of maintaining reconstruction precision, the computing time can be shortened remarkably, and the alternate iterative algorithm is suitable for large-scale field inversion computation.