Abstract: Tidal couplet thickness variation and its genetic mechanism are studied through smoothing processing, Fourier transformation and wavelet analysis for the cores taken from the Well A located in the Pearl River Mouth Basin. We compared the thickness of sandy and muddy laminae with the couplets thickness. It reveals that the thickness variation of sandstone and mudstone is not only controlled by the tide cycles, but also affected by the changes in microfacies and event deposits. The tide cycles in high frequency, works like a sinusoidal wave, of which the affects to the thickness of sandy laminae is small. On the contrary, facies changes have great influences on the thickness of sandy laminae, even the frequency of the changes is low.