Due to the topographic effect of the Tibetan Plateau and its vicinity, some small but strong high and low pressure systems often occur on the isobaric levels of the lower atmosphere by extrapolation, and the real systems cannot be reflected clearly. Therefore, it is still a difficult problem to analyze and diagnose the vortexes near the surface of the Tibetan Plateau with current isobaric analysis methods. In recent years, there has been significant progress in the numerical models, but the problem of weather analyses near the surface of Tibetan Plateau is not yet solved well. One of the reasons is that the pattern of geopotential height contour on the terrain following σ coordinate commonly used in models is similar to the topography and cannot represent the synoptic systems. In the article, a new variable, which is referred to equivalent isobaric geopotential (øe) and satisfies quasi-geostrophic relation, is introduced based on the averaged harmoic-cosine vecter decomposition in a limited region. It can be used in the same way as the geopotential used on p coordinate. As an example, a eastward moving Tibetan Plateau vortex is analyzed. The results show some small but low and high systems always exist over the Tibetan Plateau due to extrapolation in the sea level pressure field, but at σ=0.995 level, the process of the eastward moving Tibetan Plateau vortex coupling with the southeast vortex at lower levels can be depicted well by the distribution of øe, and these artificial systems in the Tibetan Plateau disappear. Therefore, the weather system near the surface of Tibetan Plateau can be analyzed well with the analysis method of equivalent isobaric geopotential height. On the other side, the distribution of øe can link the synoptic pattern over the Tibetan Plateau with that in its lower reaches, which is favorable to reveal how the systems over the plateau impact the weather in the lower reaches.