Fatigue tests in terms of high cycle of 107 and low cycle of 105 at 150 ℃ were carried out for the samples from gravity-casting C14 cylinder heads of AC4B aluminum alloy.The low cycle fatigue strength and high-cycle fatigue strength of AC4B aluminum alloy were presented by non-linear fitting and statistical method.The results show that high-cycle fatigue S-N curves follows second-order exponential decay form

meeting the "limited fatigue limit" condition

while low-cycle fatigue S-N curves is characterized by quadratic form.Low-cycle fatigue strength and high-cycle fatigue strength obtained are consistent by two kinds of ways

which shows that the analysis method is rational and reliable.Fatigue strengths of samples involving the low-cycle and high-cycle both meet the new Sail cars safety and reliability of Shanghai GM.