Objective The conductivity in bioelectromagnetic parameters is directly related to the functional information of the tissue, and precise reconstruction of biological tissue conductivity is of great significance in the fields of medical imaging technology and medical diagnosis. In this paper, the microwave-induced thermoacoustic tomography (MTAT) algorithm is improved to improve the reconstruction accuracy of tissue conductivity.Methods On the basis of utilizing the finite element discrete method to solve thermoacoustic wave equation and Helmholtz equation, an improved method of quantitative reconstruction of biological tissue conductivity based on regularized Newton iteration method (RNIM) is proposed in this paper.Results The effectiveness of the algorithm improvement was verified by numerical simulation and phantom experiments with different concentrations of NaCl solution. The results of the tissue phantom experiments showed that the relative error of the phantom conductivity quantitatively reconstructed by the regularized Newton method is significantly lower than that of the quantitative MTAT with fitting, for the cases with different target positions, sizes and contrasts. And the accuracy of the reconstruction is improved. Simultaneously, the RNIM method was used to reconstruct the conductivity of a single target with the same concentration at different positions with smaller variation in the mimic experiments, as well as the relative ratio of the reconstructed conductivity of multiple targets was closer to the actual one, which the experimental results verified the stability of the improved method.Conclusion The results show that the optimized algorithm reconstruct the conductivity of the tissue phantom more accurately and quantitatively, which is of great significance for the early screening and precise diagnosis of tumor localization and staging, to prevent the deterioration of the disease.