Abstract: The severe accident experiment Phebus FPT3 was simulated and analyzed by using MECLOR1-8.6. The fuel rod behavior, the hydrogen production, the release, transport and deposition of fission products, and the thermo-hydraulic condition in the containment were calculated. The comparison between calculation results and experiment data shows that the rod behavior, the hydrogen production time and trend, and the thermo-hydraulic condition in the containment fit quite well. But the total quantity of hydrogen production and the fission product relative data have some differences between the calculation results and experiment data, because of some limits of the model in the code. The calculated total quantity of hydrogen production is smaller than that of the experiment, and most of the calculation results about the release and deposition of the fission products are a little bigger than those of the experiment. Besides, the accuracy quantification of the calculation was evaluated with the fast Fourier transform based method (FFTBM).