Abstract: Reservoir water temperature has been calculated using Zhu Bofang's method and statistical analysis method and compared with the measured temperature in the case studies of three typical reservoirs in cold region. The results show that for the water temperature in winter, the statistical analysis method is better while in summer, the results of both methods are close to the measurements. For the autumn and winter seasons, neither of these empirical formulas can take into account the mixing phenomenon driven by instable stratification. Overall, the statistical method, though better than Zhu Bofang's method, still needs further modification. We have examined the causes for its deviations in temperature calculation and developed a correction method and corresponding procedure for calculation of the effects of vertical mixing in large water bodies. The corrected results are in good agreement with the measured temperature. The statistical analysis method after correction shows a better accuracy in calculation of the water temperature in reservoirs in cold region. The results would help temperature control design and operation management of concrete dams.