The accuracy of thermal parameters, which are one of the important conditions to study the problem of temperature control and crack prevention of concrete, directly influence the calculation of concrete temperature and stress field. Based on basic genetic algorithm, the FORTRAN procedure was programmed after improving its defects. According to a project, the temperature test was carried out in one of sections of a prototype concrete structure, and the measured temperature dates were obtained. Based on the improved genetic algorithm and the measured temperature dates, the thermal parameters of concrete were obtained after back analysis, and the calculated and measured values were compared. The results show that the improved genetic algorithm provides a effective way for back analysis of concrete temperature field.