Variable crosssection ring sealing surface contact boundary is waveform curve,oil film thickness between dynamic sealing surface at circumferential and axial is changing,the existing research is failed to better reveal the dynamic characteristics of this kind of sealing ring lubrication.The three dimensional(3D) model was established which mapped changing of crosssection along with the waveform.The variable crosssection seal ring elastohydrodynamic lubrication（EHL）numerical calculation program was written based on ANSYS software APDL language,and the iterative solution between the lubrication equation and the elastic deformation equation was realized.The 3D distribution of oil film pressure and oil film thickness,as well as the relationship between the distribution law of oil film thickness and the side curve of lubricating oil film were obtained.The influence of initial compression ratio on the oil film thickness and distribution was researched.The results show that the thickest oil film of the dynamic seal appears in the sealing surface wave peak,and the thinnest oil film appears in the sealing surface wave trough.It is not full film lubrication between the sealing surface of crosssection ring sealing with the axis,and oil film rupture tends to occur more at the axial outer boundary and the wave trough of lubricating curve.The initial assembly compression ratio has quite large influence on the oil film thickness and distribution of the dynamic seal,too large or too small initial assembly compression ratio will result in poor sealing effect.