Accelerate mass spectrometry(AMS) has been used to the measurement of specific activity I(³⁶Cl/Cl) of high purity AgCl made of “nducing-adsorbed” ³⁶Cl(and Cl) collected and purified from the surface of young marine sediments. Sediment age(t) was calculated from closed specific activity I₀(³⁶Cl/Cl) of sediment grain based on the radioactive decay law I=I₀^e-λt.The study shows that the specific activity I₀ of closed ³⁶Cl in earlier marine sediment has linear relationship with latitude. And taking account of latitude factor, the proportionality constant of specific activity-yield (μ) was obtained as 23.652 38. ³⁶Cl specific activity of two sediments grains and a manganese nodule from seabed has measured and the ages of sedimentation for the samples are 83.2×10⁴ a, 74.0×10⁴ a and 17.6×10⁴ a, respectively. The calculation method of I₀ is of scientific foundation and accessibility and it can provide the exact sedimentation ages and explain the correlation of marine sediment layers.