Abstract: Accelerate mass spectrometry (AMS) has been used to the measurement of specific activity I ( ³⁶Cl/Cl) of high purity AgCl made of "inducing-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=I₀e^-λt. The study shows that the specific activity I₀ of closed ³⁶Cl in earlier marine sediments has linear relationship with latitude. ³⁶Cl specific activity I_L from typical and uncontaminated seawater of the Pacific Ocean (4°18'N,161°09'E) surface was measured by AMS and the result was 99.34±10.30. And taking account of latitude factor, the proportionality constant of specific activity-yield (μ) was obtained as 23.65238. 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.