A non-invasive in vivo monitoring method of tissue thermal coagulation based on optical tomography was proposed. The nonlinear multi-parameter optimization algorithm in the new reconstruction method was proposed,which was not based on the calculation of Jacobian matrix. N-decimal system parted coding operator genetic algorithm was used as optimization algorithm. The new reconstruction method could improve the reconstruction speed,avoid the ill-conditioned problem and calculation error of Jacobian matrix. A simplified region of interest model of thermal coagulation was given,which came at the least price of reduced precision. The monitoring method was proved by the experiment of egg white. The curves,reconstruction images and clinic significance were studied. It can be concluded that the reduced scattering coefficient image,got by optical tomography,can be used to evaluate the process of thermal coagulation non-invasively.